I don't really consider Chesterfield's as expensive, but whatever..

You're going to have a problem trying to limit yourself to P'burg because there is not a heck of a lot that is open at night there now, even less than there used to be. Greenhouse would be a very good bet though. 2 for 1 on drinks and appetizer specials, and they have a huge bar. I don't really know Oyster Pond at all well, so don't have a suggestion there. Mark's Place is not technically in P'burg, but close and sure seems to fit the bill.