To my knowledge, there are extremely few people who have bred their striped keelbacks. Some have, but it's not a snake I'd start with.

The price of an ordinary, common species of garter from a breeder is pretty low, especially compared to what it costs to house and feed any snake, not to mention the time you will be spending on it. In the long run, the acquisition price is practically negligible and in my opinion, it's the wrong place to save money.