I think that Sako used to chamber their TRG series rifles in .30-378 Wby Mag, but I believe that that cartridge has been discontinued. If they are in good shape (98%+), and the throats aren't too badly eroded, then they'd probably be worth $800-1000 used. Before I'd buy a used rifle in a cartridge like .30-378 Wby, I'd have the bore inspected by a gunsmith to measure throat erosion. .30-378 burns a truckload of powder at very high pressures, and that's a recipe for nasty throat erosion. No sense spencing top dollar for a rifle with a burned out barrel. I'd council caution.

Mike