Hi, I'm planning to switch formula milk brands to a cheaper option, any recc?

Currently my toddler n baby are drinking the fairprice gold brand. My toddler has been drinking it well so far. But for my baby, recently she's not pooping as often and constipated. She drank the 0-6m n had no problems but constipated when she's 8m. Wouldn't poop abt 2-4 days, when she poop she would cry n sweating. I was thinking it was the cause of the milk. I was thinking to switch to either lactogen or dugro. Also, should I switch my toddler's milk? These 2 months, I find it a bit tight to continue with the fairprice brand. Anyone have recommendations? #AskingAsAMom #adviceappreciated