Some foam from another seat scored cheaply ,and a new material for the seat covers ,use the hog ring plier to secure the seat material to the metal bar at the bottom,take yer time to evenly stretch everything and you will have a new seat on the cheap.
Its like 170 bucks for a new seat material,30 bucks for the hog ring pliers,and whatever price you can get a donor seat for that has good foam on it.
I would use the old frame ,it fits and has the correct tilt and seat height for your ride.