Do not, repeat DO NOT, buy frozen rodents from Petsmart or Petco! I imagine that's what you're doing when you say 4 for $11. Those rodents are regularly freezer burned and can have a horrid smell when thawed (which no frozen rodents should). Even if you have to go to a specialty reptile store and get pre-killed rodents to freeze yourself, it's a TON better than going to Petsmart or Petco!

That said, try getting a mid-sized order from an online supplier. Yes, the shipping can be pricey but its worth it knowing you have quality food for your snake. Doing a good search and comparison of the different dealers, as well as contacting them and telling them your situation, can give you more options than you might realize.
Also, if you have a vacuum sealer of your own then frozen rodents can last up to a year. Just keep resealing them and they're good to go.