Cheapest way to fix seats with tears and missing foam?

Hi everyone I was wondering if anyone had any ideas on a cheap fix for the seats in my 75 duster. There is some foam and seat fabric missing as well as a lot of tears in the front and back seats. I was planning to fill the missing foam in with glued in pieces to get the shape and then trying to stretch fabric over that to keep it as cheap as possible while still functioning and protecting the foam. I originally planned on covering the foam with an aftermarket seat cover and cutting and sewing the middle section to allow the seats to split but figured it wouldn't last as long as a car seat fabric. I'm open to any ideas really, I'm not too concerned with looks right now, just functionality; I still have a lot of work before it would be any type of show quality. Any help would be greatly appreciated!