Adding to what russ said, I would say it's important to know what a gun is worth in your area
. For instance, I see Glocks selling in south Florida for $600, but here in north Florida, they run about $100 less.
Look for a local/regional gun forum that has a buy/sell/trade section. If you monitor that, you'll see what things actually sell for around you.
Regarding gunbroker, most gun shops will do transfers. They always charge a fee. First, they have to pay for a background-check phone call. Second, they are in business to make money. Third, they will start smelling funny to BATFE if guns are going through the place and no money is changing hands. Some shops, though, charge a percentage of the sale price of the gun instead of or in addition to a flat rate. So ask first! Around here, transfers typically run between $20 and $35.
There's a feature on gunbroker that will let you enter your zip code and search for FFLs in your area. Most of them list their fees. You can find it here