I'm assuming you mean a older style Acat that is minimum weight and has a carbon mast?

You can find these from between $3 and $12k, depending on age, and how they've been used.

All glass older boats are less, as they can get soft over time, kevlar and carbon boats hold up better over time, so expect to pay more.

Older Catnip style Acats with aluminum masts can be found for $2-$5k.

I saw a boat that Steve Clark built and sailed in the worlds (not the recent worlds) with a carbon hall mast for $3k in RI, nice boat, carbon daggers, rudders. It was about 5k over weight, but the daggers were solid and you could easily get the weight out of the daggers. This boat was at Sail Newport, dont know what happened to it.

Also, the Lake Hopatcong guys have a bunch of older catnips, some are projects, but you might get them to part with one of those boats. They use these to introduce people into the class.

The other option is to build your own, I spend $11k on my boat, and its a current design.

Check here, lots of newer onew for sale now that the worlds is over. http://www.usaca.info/

Bill