Where can I find foam to replace a couch cushion thats not terribly expensive?”
I have seen upholstry foam at Joann’s Fabrics. Any other large fabric store should also have upholstry foam. You could also try going to garage sales, and finding a cheap chair and taking foam out of it. Also, my mother inlaw one time used to sit on pillows, and when she reupholstered one of her chairs, she put a pillow in it.