Why are seats such a pain?

I need a drivers seat for my s13 it’s literally the last piece I need. I’m not picky I just want the least expensive option all of the one seats I’ve found are like $500+ and I can’t for the life of me find a seat rail that’s not 400 bucks and a seat on top of that. Does anyone know if I can buy and oem seat rail and fix it to an aftermarket seat?