The company I work for owns a subsidiary in Cartago, Costa Rica. I go down there every three months or so. I like to stay at Hotel Bouganinvillea in Heredia province of San Jose. They have nice rooms and are quite cheap. Easily could fit a family of 5 in two rooms.
I'm not quite sure about all inclusives as my company outsources our travel through a company in Chicago where we're headquartered.
However, I would just make sure that you be careful while driving, as street signs are mere suggestions rather than ones that everyone obeys.
If you have any questions about Costa Rica, I'd be happy to tell you what I know. I also have a gallery of pictures on my personal website that I will give you the address to if you wish to see the pictures I took last time I was down there.
http://www.hb.co.cr/