For an AK style, Real Sword is a hands down winner. For M4, I'd highly recommend the Classic army M15A4, though that might be slightly outside your price range. Then again, the Real Sword Type 56 might be as well.
I did extensive research and settled on the Tactical Carbine version of the Classic Army M15A4 (basically a full stock m4) as my first gun. If an Armalite is what you're looking for then I think it's the best of all possible versions. You have the shortened M4 carbine barrel, which makes you less likely to smack your barrel off something when turning quickly, combined with the full stock which houses a large battery. Small batteries don't have near the run time of a large battery, not to mention that the reinforced slip ring (the ring that keeps the fore-grip on) is really strong. While this is mostly a good thing and a big step up over CA's previous M15 versions, it makes changing small batteries in the field very difficult if not impossible.
CA's M15A4 series in general is a big step up over their previous versions and as far as stock armalites go they're probably the best. All metal where the real steel version is, the plastic parts where the real steal version is plastic are made of high quality enhanced nylon fiber rather then abs for great texture and feel. Classic Army has a deal with Armalite so you get all the proper markings. Plus that deal also goes to show the quality of the manufacture, Armalite wouldn't put their name on a shoddy product.
Internally the gearbox is reinforced metal and all the gears are metal as well. It fires hotter stock then Tokyo Marui's as well, firing at 300-320 fps where your average TM only fires 280-300 fps.
All in all this is a great starter gun if you can afford it. Because it's all metal you don't have to worry nearly as much about breaking it and you won't get any of the wobble or creaking that is infamous in older stock TM M4/M16's. Unfortunately affording it is the biggest problem, they're not cheap. For reference I got my CA M15A4 from the classifieds, upgraded with a bunch of Systema internals to fire 390fps, for $600 shipped which was a great price.
As you can probably tell, I'm a big fan of Classic Army. One thing to keep in mind about Classic Army is they now have two lines, a proline and a sportline. Originally they were easy to tell apart because the proline had the metal body and the sportline had a plastic body but recently CA has been releasing their sportlines with metal bodies. The price tag should still allow you to easily tell the difference, the sportline being $300-400ish and the proline never being cheaper then $500, usually more like $600 or more but it's still something to keep in mind. All the pros that I went over above were regarding the proline model. The sportline model has cheaper everything internally and externally.
There's alot of people that will expound the virtues of G&P as well. And I'll admit the externals of G&P are very nice, easily on par with CA, in some cases better. The reason why I don't say G&P over CA though is much the same reason why people weren't big fans of CA up until a few years ago: their quality control for the internals is not the greatest. That means a fair number of lemons. CA got a handle on this a few years ago and they've been making great strides in terms of their rep ever since, but G&P isn't quite there yet. This is simply my personal opinion and there are many people that would likely disagree with me, but it's something to keep in mind.
I should probably give TM some love here as well: Due to Japanese laws TM guns fire alittle cooler then most others and their externals are going to be almost entirely abs plastic. But *nothing* beats TM for internal reliability. You leave a TM stock internally and it will last for literally decades.
One of the perks of going with an M16/M4 variant is that mags are dead easy to come by and dirt cheap. You can get Star brand mags for like $5 a mag or less, plastic yeah but sturdy none the less (Star is also one of the few brands that makes realcaps too). Metal mags will run you a fair bit more, $15 to $30 a mag. There's no real reason to go with metal over plastic for mags except looks/realism. Though of course if you're going to go hicap then you might as well get metal ones. As to Brands, TM and CA make good mags. I've heard pretty good stuff about MAG brand mags as well. King Arms not so much, especially for M4/M16 mags. Star is always a good affordable fallback too.
Some people say you need to shell out for batteries, mags, camo, chargers and ammo in the begining. Most of that isn't necessary right off the hop. The stock battery will do you for awhile. Most of the guns come with a hicap (high capacity (300-600 rounds)) mag that will also do for awhile. I do agree that a good charger would be a sound initial investment, but not a total requirement, especially if you plan to get a good battery down the road and don't care if the cheap wall charger fries your stock battery. Camo isn't really required in the beginning either, just some dark clothes. Ammo, yeah obviously a requirement but even good ammo (BB Bastard) only costs $10 for two thousand rounds.
So truly, all you really need to start is the gun, a bag or two of ammo, good eye protection (which will run you between $30 and $50) and decent footwear (combat boots are the best but $40 hiking boots from walmart will do in a pinch). That said, if you can afford it then it all helps. Camo would cost about $100, a chest rig or vest would cost another $100. A good loadout of mags, even the cheap Star mags, are going to cost at least $50. A good charger is at least another $50, with another $50 for a good battery. A sidearm is another thing that people like to have but isn't really necessary. A decent sidearm would cost you between $250 and $350. Probably another $100-150 for a duty belt, a holster, a sling, gloves and a misc pouch or two.
Sidearms aren't really required right away so if you're on a limited budget then hold off on the sidearm for now. If you have the budget for it then what you want in a sidearm depends on two factors (besides cost of course) whether or not full metal is a must and exactly what model you're partial to. Certain manufacturers tend to make certain models better then others. If full metal is a must then the best choice that isn't going to cost you an arm and a leg is probably KJW, especially for the M9 which they do very well. You'll see alot of WE's around, they're cheap and full metal but tend to have problems, especially their 1911 models. KJW has a rep of having mag problems, but I have had two KJW pistols and I haven't had any trouble with my mags. If full metal isn't a must then WA or TM would be very good choices.
As you can see from the above (very rough) prices, airsoft is not a cheap sport. It's generally accepted that the absolute minimum you need to get into it is $500, and it's usually more like $1000-$1500 if you go with quality gear. I've seen a few people do it for less then $500, but it takes a fair bit of time, effort and jury-rigging. And of course quality tends to be a problem at that level.
Now for some gun pron:
My Classic Army M15A4 Tactical Carbine without external addons:
My baby, CA M15A4 Tactical Carbine with m203 grenade launcher, red dot sight and taclight: