Store Brand Formula

My baby is 5 months old and since the day she was born until about 2 months ago she was drinking Similac Neosure because she was premature. Before switching to her current formula her doctor and I tried a few other Similac products and they all made her sick and fussy. Right now she is on Enfamil Gentleease formula. She is doing great on it but WIC refuses to cover it. So i am having to buy it. I have seen a few store with their brand if it and its a lot cheaper. Has anyone used store brand formula? I wanted to breast feed her but my milk never came in. And she was to little. So formula was my only choice.