I went down that path about 2 years ago. Working from home and generally being a homebody, I’m basically on wifi all the time. I made the switch to Ting (from Sprint) and pay $15/mo, maybe $20 if I go over my 1GB data on 5G (I have alerts set up). It’s not ideal if you drive a lot and stream music on Spotify or whatever (or if internet/power goes out), but if you literally have no life, don’t go anywhere, and basically have nonstop wifi, Ting is pretty cool. It uses T-Mobile towers, so your mileage may vary. There’s a few places it gets a little fucky, but it’s been pretty reliable overall. I thought about looking into Mint recently, but decided not to even dive down that rabbit hole.
I feel like logging in with Facebook and Google on sites is just as much about them gaining access to scrape more info about you as it is for your “convenience.” While there could be value with Lemmy, it’s not nearly what it is with Facebook and Google. So I would say not likely.