Long before the current downturn in the market when most people didn't know what a short sale was, people brought money to the table when they owed more than they could get for their homes. Agents bring value to a transaction. A good agnt will maximize your price, terms and final net. Trying to sell by owner limits your market to buyers looking to save themselves the commission. Using a limited service company may leave you exposed in some areas of contract expertise and negotiating against professionals.
I'd suggest getting the best agent available and try to minimize your loss or stay put for a while. Sorry.