I'm one of those guys in Fleet 32...
A 20 in good shape with everything could be $4500 or so, but if it needs a tramp, sails, rigging and general work, it could be $1000-1500. Parts for them aren't cheap.
If it has solid beams, then that adds a lot--the telescoping trailer is nice, but not necessary.
Check out the forums at
http://www.aquarius-sail.com/ to get more focused info. Someone may know the boat and could give you more info.