Hey I am having the same problem you are having but here are a couple of Ideas I have came up with.
1. Playin lazer tag and goin out for pizza with my boyfriends and some friends then haveing my girlfriends stay over and camp out. (i have alot of land too)
3.A place like fun plex or something. Like an amusemnt park. (I dont know how far you live from one of those)
5. A bunch of friends stay at a hotel. (just everybody pitch in a lil money to help pay for it)
Well thats all the ideas I can think of for my own party so I wish you the best of luck and Ill be checking in here to see what youhave decied on!!