Nice first offer. Most first offers that are not at minimum price on sedo have a serious buyer behind them (from my experiences). I would counter offer, doing this you do run the risk of losing the sale altogether.
Basically, if you are happy with $250 for that domain and could use the $ - take it. If you are not in need of cash and are not happy with the offer, counter. Pushing this domain to auction would probably not be very successful (IMO). Good luck either way!