I have ordered from them before and got the same answer on the phone.
Because they charge actual shipping rates, not some bogus handling charge and shipping.
I think the going rate for a pistol is $30-35 from most sites. So I would consider $20 a bargain. Bu you are correct UPS/FedEX/USPS are going to charge you air rates and more than likely the package was never put on a plane between NC and SC.