Well, that era Gibsons are pretty collectable, even the plain models (the Mastertones were the better ones, but the simple-tonering and no-tonering models are vintage, too). You haven't said what model this is. If it has a tonering (that metal rim UNDER the head, that the stretcher-band is pulled down onto by the brackets) then it's more valuable than if not. If that tonering is round and has 1/4" holes in it, it's worth its weight in gold, 'cause that's the Mastertone tone ring. If there's fancy inlay on the fingerboard, it's desirable.
I don't know today's market, but a guess would be:
Mastertone model (TB-3?) with nice inlay -- from under but near $1000 to $3000 or even higher. Simpler models (TB-1 or -2?) with plain dots -- around $300 to $1000, maybe a touch more.
I'd check and see if any have sold on eBay auction recently. The prices on eBay are sometimes high, since it's an auction and people get "caught up" in it, but it's also a good "leveler," unlike vintage instrument dealers, where you have no comparison shopping possible.
If I can find out more, I'll let you know.