OP - there are many group tours out there and I can tell you from being in the industry, none of them are as cheap as what you think they should be. The prices American's pay is literally dictated by the two government's right now and there are still changes made seemingly daily. I have stayed relatively current on the situation.

There are many, many choices out there. Cultural Cuba, International Expeditions, Natural Habitat, National Geographic, Globus, Backroads, and many more. Not all are equal. Also, I don't recommend going on a tour with over 25 people. It is such a canned experience and not the reason most want to see Cuba. Just my opinion though.