Walmart and Target brand formulas?

So I am exclusively pumping and up until now I have been able to make just as much as my baby girl is eating, sometimes making over so I have a small freezer stash. Unfortunately within the past week or so it looks like my supply is becoming low no matter what I do, to the point I’ve had to dip into my freezer stash a couple times. I’ve upped water intake, body armor drinks, lactation bites, heat before pumping, power pump sessions, you name it I’ve probably tried it. My husband and I are wanting to start supplementing with formula when needed to make up for what I’m not making. Obviously formula isn’t cheap, especially when breastmilk is free. I have been researching both Walmart and Target brands of formula to help save on the cost. We have no problem getting her the more expensive brand if necessary, but would like to start on a cheaper brand and see if she can tolerate it. Baby girl does not spit up from my breastmilk often and when she does it’s usually once and only a little bit. She does also have the occasional fussy and crying periods but nothing extreme. Do you mamas have any suggestions or input in relation to the Walmart and Target brands of formula?