Are you SURE it wouldn't be worth it to buy frozen online & have shipped? Even for just one snake, you can buy at least a year's supply- they won't spoil as long as they stay frozen, & they keep even better if vacuum-sealed. Some sources sell them that way, but otherwise, you can do that yourself too, with a "seal-a-meal" device.
Probably better than confusing him with mice, he might be hard to get back on rats. They're usually cheaper online, but even when you figure in the shipping (& gas & inconvenience of heading to the store all the time), I bet they come close to costing the same? And if you know anyone near you that keeps snakes, maybe you could split the order too?