Hi Brittany,
Trout, salmon, perch, bass, pike, sunfish, and pollock are commonly available fish that are good for your snake. I'd suggest catching a few extra trout in the spring or fall and vacuum seal, then freeze them to get you through the winter. I imagine that one salmon would last you all year. There's no need to go for the expensive kind. Chum are fine as long as your snake doesn't turn its nose up at them
.
Rick