Honestly, it would depend on the buyer. If the buyer REALLY wants a specific gun, they would offer more. But for the most part it goes something like this:
AP Guns usually start off around the price of about $15 per gun. AP Pistols would be worth around $5 to $10 each. They are certain AP guns that might have more value due to how rare the gun is.
An account with FG42, Mosin, Python and S&W M29 would be worth around $50.
The price of the account also depends on the seller. How fast they want the money, if they care they're losing profit & are they in need of money.