If you're only willing to spend abotu $150 on weapons, go to canadian tire or wal-mart. Most weapons that are field worthy, and by field worthy I mean 280FPS with 0.20g BBs, clearsoft, and pretty much 75% plastic, still run you about $250.
Sometimes there are local shops with guns that aren't horrible. Example: I got my Cybergun SiG552 from a somewhat local store (I travelled about 2 hours). Performs sub-par. Required some minor upgrades to get it to my idea of "on-par performance".
Since you said you want to play in a forest (Right off the bat, unless you OWN that land, don't play in there. All it takes is one guy to walk by, sees someone in the bush with a replica firearm, and you have swat teams surrounding the bush) you're probably going to need something a little more powerful than Wal-Mart guns. Reason: You won't even cut through the leaves. Literally. Your BBs will just bounce off probably, or at best, lose trajectory. Unfortunately, Airsoft isn't the hobby/sport in which you can be tight with a budget.
What I've spent so far in about 6 months...
SiG552: about $335.00
Mags: about $80.00
Two Inner Barrels: about $80
Metal Hop-Up: about $35.00
New battery: about $40.00
Surplus Woodland BDU: Like $40.00
Drop-Leg Panels+Pouches x2: about $80.00
Hat: Uh, $10.00
Balaclava+Gloves: About $45.00
So $745.00, roughly, give or take $10.00. I just placed an order for a vest, that was roughly $53.00, and I'm also purchasing 4 more mags+oil, and that's another $70 or so. After that, about $250 worth of internal upgrades still needs to be made to get the gun to my idea of "fully operational". All that is raked in at $1,118.00. and I still plan to get a headset for communications.
By no means am I trying to tell you "spend more or you suck", there are people who play airsoft just to shoot each other. Hell, me and my brother do a newbie-day style game every so often, and we just hand out the Wal-Mart M4s, and they play in whatever they're comfortable with, which is usually just jeans and a sweater that'll give them some kind of camoflague.
Honestly if you're just looking to shoot each other for fun every now and then, though, I might recommend paintball (unless you did that and hated it) just since it's a more casual sport. You can rent guns at fields, don't have to even wear appropriate gear, and you don't spend nearly as much. Especially since there's not a lot of real "Airsoft Fields". That and paintball games can be very last minute.
Although nothing feels quite like shooting your buddies with a gun that looks like a real gun.
Primary: Custom WE M16A3
Secondary: KWA MP9
Side: Custom WE M1911A1