Google Fi? That only works on Google phones though.
I'd also check out Ting, my DH and I used them and really liked them. They run on the Sprint network.
Most alternative providers run piggy-back on the large networks (At&t, sprint, verizon), they pay "rent" to the big guys for use of their towers. If you know which big providers have coverage in your area, you can try googling for alternative providers running on their network.