First of all, I am not a huge fan of J-30''s. They are have cramped cockpits and poor deck layouts even in the current optomized forms. They are notorious for having mega-huge areas of core rot in the hull and deck.
When I think of what I would expect in a J-30 that is for sale for in the Carribean for $7,500. I would expect that it would need to have large sections of the hull and deck recored. Standing and running rigging is probably shot. The engine is probably in need of at least a rebuild. The sails are probably well past useable condition as a raceboat or worse. I''d expect that the interior is probably a wreck and the woodwork needs serious attention. Fuel and water tanks could be at the end of their useable lifespans.
Now, if you add some proportion of all of this up, figuring that you can buy things at cost and do your own work, I figure that you could still easily buy a J-30 in near perfect shape for less.