2015 mitsubishi mirage

I have 70k miles and would like to get my transmission flushed/exchanged and one shop said they only use mitsubishi brand for $300 and another said Valvoline cvt fluid is compatible and would be $150. I want to do what's best for my vehicle and not fuck it up, but obviously would prefer to save money if that is a feasible option. I don't want any transmission issues but the confounding info is confusing me and I don't know if I'm being ripped off by the shop saying mitsubishi fluid is the only fluid