What is the cost of a MacBook 13" battery replacement?

You can get a new third party battery fairly cheap on eBay. Every MacBook from 2006 through Mid 2009 except the Late 2008 Aluminum Unibody and the Late 2009 and 2010 White Unibodies use the same A1185 battery.

Black Batteries http://shop.ebay.com/i.html?_nkw=macbook+black+battery&_sacat=0&LH_BIN=1&_sop=12 &_dmpt=Laptop_Batteries&_odkw=macbook+white+battery&_osacat=0&_trksid=p3286.c0. m 270.l1313

White Batteries http://shop.ebay.com/i.html?_nkw=macbook+white+battery&_sacat=0&LH_BIN=1&_sop=12 &_dmpt=Laptop_Batteries&_odkw=macbook+black+battery&_osacat=0&_trksid=p3286.c0. m 270.l1313

Or for $129 from The Apple Store http://store.apple.com/us/product/MA566LL/A?mco=MTY3ODQ5OTY