All good advice so far. If you really want it, offer 1500. Use the rot as a bargaining chip. That little spot wouldn't bother me much, but as has already been said. It probably looks a lot worse on the inside of the frame.
One thing nobody has mentioned is that if the frame is rotted the tub prolly is too. Look under all the carpet. Especially the driver and pass floor pan, and below the seatbelt. Those spots rot often. Check the hard brake lines too. I've seen those just about rot off. Check the body and shock mounts too.
There is a guy near me with a '93 for sale. You can see right through the frame near the rear shackle mount. Huge peices of frame are just gone. Won't budge from 2000$. Granted he is crazy but....
Actually now that I think about it, that jeep wasn't there last time I drove past. Wonder if some poor sucker bought it.