I've been involved with combat robotics before I even was in FIRST - in fact its what has got me interested in robotics in the first place...
I've built a bunch of bots, there are a TON of weight classes:
Antweights - 1lb. some of these bots are insane, they can do so much damage and have so much power yet only weigh 1 pound...
Beetleweights - 3lbs.
Hobbyweights - 12lbs.
Featherweights - 30lbs.
Lightweights - 60lbs.
Middleweights - 120lbs.
Heavyweights - 220lbs.
Superheavyweights - 220lbs.+
Actually, combat robotics can be a lot less expensive than FIRST. The electronics are simpler, for even a HW robot can run on Victor 883's for the motor controllers. Most bots run a signal booster attached to the Victors, then controlled with a simple FM or PCM hobby radio system. Also, there are no specific components that need to be used, most builders can pick up parts at Surplus stores, their garage, even Kmart...
And lastly, competitions are a lot cheaper than FIRST, usually between 5-20 bucks depending on the weight class.....
If anyone wants to check combat robotics out, I HIGHLY suggest building an antweight robot. They are very inexpensive, they generally can cost about 600 bucks for an ellaborate robot w/ a radio transmitter, but can cost as low as maybe 2-300 bucks for a simpler one. They also are quite easier to build, as in antweights you can get away with duct tape, loctite, or even hot glue on the components of your robot.....
Check out
http://www.robotmarketplace.com they have some nice ant kits and lots of other cool robot things.