Even online with shipping I pay around $1 per mouse, but the quality is so high. I've had them last me 10 months, though I prefer to use them up in 6 months.
A couple of tips, get some Ziploc vacuum bags with the hand pump and repackage your mice in smaller quantities. Then put those bags in another bag or a Tupperware type container. What I like about the hand pump bags is that you can open and reseal them. I got mine on Amazon. They probably cost a little more there, but I didn't have to run around looking for them.
Another tip is find another snakekeeper or two and order together to share those shipping costs, but I admit that one is pretty obvious. I've bought from two suppliers, American Rodent Supply at a show, and Layne Labs via FedEx. Last time I looked into others but went with Layne because you can get bags as small as 10 which is great for growing snakes, and their facility is so clean that they do not need to have their mice irradiated.
Sadly it will cost a bit more to the East Coast. I do suggest you look at ARS as well and I hear great things about Big Cheese down in TX, across the board. I considered both of them this time, but Layne won for flexible, least wasteful package sizes. $112 including shipping feeds my three for 6 to 8 months.