Angie, I was in Costa Rica for a couple of weeks last winter. I was on the Pacific coast, so I don't have any firsthand info on the east coast, but to the best of my knowledge there isn't much(if any) of a bonefish fishery in Costa Rica. The east coast does have good populations of snook, tarpon, and other gamefish, and the Pacific coast is famous for it's offshore fishing and also has inshore fishing for Roosterfish and miscellaneous Jacks.
If this is to be a trip to fish solely for bonefish, I think you might do well to look elsewhere(Belize or Mexico perhaps?). If you're going on vacation and hoping to do some fishing too, then Costa Rica could be the ticket. It's a beautiful country and the locals(Ticos) are incredibly friendly.