Theres O. aestivus, but the differences between the two are minute. You can buy them online from a number of places for less than 20 USD, but most are WC, and filled with probs. From what i hear they are hearty little snakes, and do excellent on a strictly insect diet.
Garters DO eat insects, but only at the juvi/subadult stages, from there they move onto frogs, mice, fish etc.
I got a bunch of snakes and a bunch of guns