I've done both. If you keep looking at used sail sites, eventually you can get a really good deal on a sail that's in next to new condition. I recently bought a mainsail that I suspect came off an A35 or something very close. 8 oz material, triple stitched, it sail looked like it was never used...for $250 bucks! I recut/sewed it for a heavy cruising sail, dumped the hump, added some extra heavy patches and a reef point. I also sewed a kit from Sailrite for a trysail. It is a very nice, extremely well designed sail which I hope to never use.
+1 on the little sailcut program above. My next sail project is going to be a new storm jib. Once you learn the basics of sail-making and have a good machine, you can save a LOT of money.