If you lived in my area (Plano, TX), I have a good upholsterer who has made some excellent cushions for us and the price was fairly reasonable IMO. You have to buy your own fabric which is where the cost comes. If you check with work rooms used by interior designers, sometimes they sell remnant rolls that are enough to do one or two chairs.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.