We also started our girls on Iams. We had Sadie on the large breed until we got Cincy and because it made her stools soft. Then we switched to Iams lamb and rice. We noticed this gave them awful smelling gas and stools. We switched them Sensible Choice, made by Royal Canin about 3 months ago and that has worked out really well...the stink is gone and the girls love the food!
I would take others' suggestions and check into something on line. If the shipping is too expensive maybe you could by large quantities to limit the trips needed to the pet store. I feed my 2 lab mixes each 3 cups a day and a 20 lb bag lasts about 10 days. If you could get a 40 lb bag, with one dog it should last about a month...Good Luck!!!