I'll check out the other boats. I have seen the Nirvana on eBay a lot and was curious. I got the Fast Cat catamaran for about $80 on eBay a few years ago and just decided to build it. They are much more expensive new.
The Footy is a fairly new class and is a real "box rule" open class. They fit in a box that is 12"x12"x6". The hull and keel have to actually fit in the box while the rigging can stick out the top as high as you want it. There is a concession for the steering and bow sprit and you are allowed a bumpkin.
They say you can make them for under $100 with a radio, but mine was a lot more. The green boat above is my first Footy. I downloaded the pattern, cut it out in model plywood and glued it together. The keel and rudder are carbon helicopter blades. The mast and booms are carbon, too. The bulb is an 8 oz sinker. I bought the sails in the picture above, but I built the one below out of the film florists wrap flowers in. It has carbon battens.
Class rules allow for two sails, one that is 12" or under (height above the deck) and the other is unlimited.
Btw, the door it is sitting in front of is a really small door under some stairs--it doesn't make for a good frame of reference on how small the boat is.