300 would be a GREAT price
I was thinking more in the 4-450 range... keep in mind if you ordered/bought it on line (across state lines) you are going to usually have to pay shipping...then pay the FFL dealer it's shipped to to fill out the forms and ontop of all this is the hassel of getting the 'cash' to the seller, the worry about if they are ripping you a new one, then the time to go and pick it up.
I have bought a number of guns this way...both at gun shows and 'on the street'. I've never thought I was buying a stolen gun or buying from a criminal...in fact in most of these types of transactions there is an informal back ground check between the two parties... who are you? where do you shoot... ect. I've even had a guy ask me to fill out a form/bill of sale and put my drivers liscence and CWP number on it.
I think the ability to pay in cash, look him in the eye, shake his hand and walk off with the gun you want...is worth a hundred dollars.
but that may just be me....