I can understand your frustration at not being able to obtain rats at a reasonable price. I've lived overseas and can remember "do the best you can" all too well. In particular, having a dog in a country with no vets at the time.

Is there any possibility that you can obtain a few rats, even though they are relatively expensive? Rats aren't that tough to breed and feed, even if you can't provide them optimal (AKA commercial) feed. We had a whole barn full of them and they ate what they scrounged. If you can get a few rats and set up a colony then you're set to feed your snakes what they would do better on and possibly even sell a few to recoup your expenses.