Best way to sell low-value guns

[Scorch]

expect to get half of what they sell for new.

Probably not. You will likely get 1/2 of resale value. I offer people 60% of resale value when I buy guns of known value.
Pawn shops typically offer very low money for guns, they make their money on loan interest and get a lot of guns for essentially dimes on the dollar when people forfeit them. Their asking resale prices are almost always too high, but since they get the guns so cheaply they are often more than willing to consider cash offers unless they think they have something special.
Gun shops would rather sell you a new gun, so if they take trades you may get a fair offer on your trade-ins.