[drache]

I don't know how many garters you're feeding, but a pound of trout will last you quite a while
now, I'm estimating weights here, but an average adult garter would probably eat something in the neighborhood of half an ounce every five days or so, which would mean that you can divide your purchase price by 32 per meal, which ends up being around $ .25 every five days or so
I don't think that's prohibitive