Hey Kris,
I did a quick search for you on
http://www.dpreview.com/ and found that for $300 the two camera brands were fuji and samsung with both models having a very low minimum macro distance of under 3cm. Although I would suggest widening your search criteria by a few more features, that way your going to get more bang for your buck even if it's just mainly for taking tank shots. So if you still haven't picked up a camera yet, use the above link it should help you out it making a good descion.
thanks Anthony
