I wouldn't offer another set price. You could ask the guy what he thinks the domain is worth. Judging on that, you can then send back one more email stating it is your last offer and the best you can do. No matter what you offer, he might not be interested in selling.
I had a guy who desperately wanted bestwineclub.com. He kept coming back with slightly higher offers, but none were in the ballpark of what I would accept. After his final offer, he finally asked me what I would sell the domain for. Once he heard my response (and the fact it was about 4 times what his highest offer way), I never heard from him again. He didn't have deep enough pockets for me...
On a similar note, I really want a particular domain. The guy who has it just forwards the domain to another site. The guy isn't willing to sell. (I have contacted him three times over a course of 4 years). I haven't given up just yet.