Final Fantasy I, II and III are 50% off on App Store until May 71
The first three games in the series, Final Fantasy I, Final Fantasy II, and Final Fantasy III, have their prices slashed by 50% until May 7. However, they aren't priced similarly, so you'll have to pay $3.99 for the first two games, while the third one costs no less than $6.99.
It's also worth mentioning that while Final Fantasy VI is 50% off as well, this one is part of a sale that commemorates a Final Fantasy Brave Exvius event. Final Fantasy VI is on sale for a limited time for $6.99.
If you're a Final Fantasy fan, you've probably had something bad to say when Square Enix launched the mobile ports back in the days. Still, all Final Fantasy mobile games received quite a few updates over the coming months following their release, so they have improved quite a lot and might worth a try.