If you're wanting the stock size replacement battery, you have a few options.
1) When you register your phone w/SAMSUNG, you should get a 50% OFF discount coupon code for all smartphone accessories on SAMSUNG'S webstore/website. They also have a BLACK FRIDAY event starting on 11/18/12 for registered customers,so, perhaps you'll be able to use the 50% OFF coupon in conjunction w/the sale for further savings.
2) When purchasing an other than OEM battery, whether it be standard size or extended, order directly from the source (HYPERION, GORILLA GADGETS, etc...) & avoid the no-name generics, for several reasons. The brand names typically are still less expensive than OEM while also offering NFC capability,not to mention a bit more battery life & a fairly generous warranty.
You should also be able to find discount codes for the abovementioned manufacturers for even greater $ savings.
Good luck & please keep us updated on your experience/situation.