for guns in that range, JG would bee your best bet. check out:
http://www.shootsoft.ca/store/
That being said, JG will be shooting around 350ish outta the box, so i would look out for that. JG guns are good, but you might have to replace some parts over time. furthermore, there is an 18+ rule to play airsoft. as for obstavcles, just build some bunkers, piles of garbage and broken down cars are always fun. if you really want to go all out, you can dig yourself a mini trench, or at least a defendable depression in the ground. i hope it all works out. FYI, i think there might be certain laws against starting up an airsoft field. Airsoft is NOT like paintball. there are different legality issues.