I was just in American Apparel today, completely appalled at their prices for items that were basically pieces of fabric, so I am 100% admiring this project and I am super tempted to try it myself. You did a great job - I know that if I did this, my zippers would be hideous.
While I agree American Apparel is expensive, you have to remember this is a product that is made completely in the US by workers that are paid a fair working wage. When big chain stores can offers things so cheap, you really have to think about "why". That's really where the price comes in. But of course, Kudos for finding them at the thrift store! always the best option! (Sorry for being preachy. Just had to throw in my 2 cents, for what it's worth).
Oh, by the way...awesome job!!