My dog is limping a bit

How long had this been since you first noticed it? If it has only been a few days, whatever problem he has he might heal on his own if you just wait a little longer. Since the vet couldn't see any problem, and he still plays fine, it shouldn't be anything with bones for sure. It can't be anything too serious.

If the problem doesn't go away, you might want to have the X-ray taken. How much is it for X-ray over there anyway? Can't be that expensive, can it?