Scott,

I think you have a lot of options available to you. Three people on board, however, depends on how small those three people are. Judging that you are 14 yrs old, I suspect they are smallish.

A Hobie 18 will easily manage three people with comfort enough to sail all day - there are quite a few around for sale too. It's a little more complicated because of the daggerboards but with a roller furling jib, it gives you a great power reduction option. A Hobie 16 would be a little harder to put three people on unless they were all pretty small - the 16 doesn't have a whole lot of reserve buoyancy either. Parts for either are 100% easily available.

Nacra's - size wise, you probably don't want to put three people on anything less than a 5.5 - that can be a pretty powerful boat though too. Parts are very available but a little more pricy.

G-Cats all have a lot of buoyancy and a forward trampoline! The G-cat 5.0 is a great boat (there's a fleet of them here in Columbia). If you can find one, take a look at it - it's a boat with a lot of flexibility (not to mention they're quite fast too). One just sold on ebay not too long ago. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3616058319&ssPageName=ADME:B:SS:US:1 . Parts for specific things like the rudder system are a bit tough to come by. Trampolines and sails are readily available.

Supercat 17 (if you can find one in your price range) might be an option too.