Get some Horse Dewormer from a feed store. It is oral Ivermectin.
A tube runs about $3-7 depending on the brand.
The dose is a rice grain size per rat and should be applied once a week for 3 weeks. Oral or Sub-Q is ok if you're using straight out Ivermectin and not the dewormer paste.
While I don't think it will kill your snake, I don't recommending treating the rats you're going to feed off. Just QT those rats away from the ones you're keeping and treating.
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