kind of sounds like you answered your own question.
If you can get good prices for frozen mice locally, go for it. But petstore can sell mice at 2-5 times more than what you can buy online. Shipping is an issue, mostly due to packaging to keep frozen mice frozen, and of course rising gas prices.
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The best way to go is to find a mouse breeder in your area who sells them as feeders. Thus, you can pick them up yourself and not have to worry about freezing.
10 hatchling ball pythons can eat 10 mice per 5-7 days, 50 frozen mice would only last a month, give or take so that does seem rather small amount to mail order. Most online feeder suppliers will be happy to give you a price quote for your order, including shipping (just send them an email and include your address, or at least your zip, or call). Check around your area for what prices you can get locally. Compare prices. You may find it is cheaper to buy from the local pet store...or you may find it much cheaper to order online and pay the shipping.
Another way to reduce shipping costs (and individual cost of each mouse) is combine orders for rodents with all your snake/monitor keeping buddies. If your order of 50 mice turns out to be 500 mice...shipping probably won't be much different but split 3 ways it will be much less. ANd most places charge less per mouse if more numbers are ordered at once (could be something like $.50 per mouse for orders of 1-99 and $.40 per mouse for orders of 100-499 etc)
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PHLdyPayne