I get asked often where I get my sodas. I use Coke, Diet Coke, Sprite, Water and sometimes Root Beer. Here in TN, I have to offer Mountain Dew also. It's a staple here.
I watch the sales papers from my local grocery stores. I have been able to get the aforementioned can drinks for as low as .18 cents each, which I sell all my drinks except Root Beer at $1.00. Root Beer in bottles: $2.00
About every two weeks the grocery stores will have sodas on sale. If you watch close you will find they alternate, one week this store offers a deal, next week a different store.
CHECK THE DATES CAREFULLY!!!
I have seen them sell drinks that are about to expire. I don't want these as I may hold 2 or 3 thousand cans I have bought over a 3 or 4 week period. Sometimes even more.
Sometimes you can find a coupon that has no limit and you can use those for your purchase. This is more rare, but you will occasionally run across a good coupon.
Hope that helps.