I got into the game last year. All the advice said "King Arms Full Metal M4". This was sound and useful advice. It's a solid gun, on it's second season stock from box. The internals are solid and it's a great platform to pick things up here and there and modify it as you go. I love it stock with iron sites.
The price point is amazing (around $250) and Toronto Airsoft has a deal on them right now to get a free charger. This year I plan on buying an extended barrel and a mock suppressor to increase FPS and provide some improved accuracy. Then I plan on doing a full camo paint job on it. You can do so much with the platform and the price point is completely worth it. You can spend $400-$600 if you like on JUST a gun. But you will need to get some other goodies, like solid protective gear. Boots ($150) and full seal goggles (revisions at $100) are a must, and I put a good pair of gloves ($40) right in there too. Face protection (for your teeth and ears, i use a combat wrap - about $10). You can get a good set of combat clothing for $80 and a good vest with built in M4 pouches for about $40. That will take you to about $600 and you will have EVERYTHING you need to jump straight in and start having some fun.
If your running M4 then you should grab some cheap mid cap mags ($10-$20 each) (hold about 120 bb's, get 3) and run those instead of the hicaps. You'll be glad you did when your trying to sneak around. For the real "Simulation" games, some may frown on that. Tell em to buy you 10 30 round mags and move on with your day and enjoy the GAME.
This is my M4. It's just every other M4, but this one is mine.