I had the same issue feeding my BP. The only stores I found around me carried up to large mice (4 pack) then jumped to medium rats (2 pack) and large rats (1 pack), all for $11. Pretty expensive for any budget. Luckily, BP.net came to the rescue. I was going to attend a reptile show near me and pick up some rats there for cheap, but ended up finding a rat breeder in my area thanks to a thread I started asking about prices. When he's on large rats, $5/month is much better than $44/month, thats for sure.

And shipping frozen goods is rather expensive. If you calculate it out, its just about as expensive as buying from the stores. So I'd go with a reptile show, or like mentioned above, snoop around for a herp club or rat breeder near you. Good luck!