You need the money and the firearm. You will not find anything in the Virginia statutes regarding requirements of private sales of firearms because there isn't anything in there. You must be 18 years or older, residents of the same state, not be a convicted felon, under restraining order for domestic violence, convicted of domestic violence, or have been committed to a mental institution. These are Federal Law requirements for handguns.
No paperwork is required for the private sale within Virginia. If you want to write a bill of sale, that is fine, it can be anything so long as it is signed...
I, Joe Seller, did sell on April 1, 2008 one S&W Model XXX, Serial # XXX to Joy Buyer and did receive $XXXX. Signed Joe Seller. He gives that one to you as a receipt for your money.
I, Joe Buyer, did purchase on April 1, 2008 one S&W Model XXX, Serial #XXX from Joe Buyer for the amount of $XXX and received said firearm. Signed Joe Buyer. You sign that one and give it to the buyer for a receipt for his gun.