Either the freezer section at costco with will generally get you 12 lbs for around $16-$18, or during the summer you can get them at the grocery store (randalls/ tom thumb, kroger, walmart, ect...) for $1/ lb or under.
If you find a deal then be absolutely shameless!! Last year I got around 15 lbs worth at Randalls and then went to kroger for another 10. You can generally find the same deal for Cherries, Blueberries, and Blackberries. The exceptions are Cranberries and Plums.... their even cheaper! I caught Cranberries at Aldi for 29 cents for a 12 oz bag, and plums at Market Street(Sort of like a Whole Foods) at 8 small plums for $1.
The only thing is you have to be willing to wait for them to go on sale in the spring and summer, which is theagonizingpart. Good hunting!