give these guys a look
http://www.justdifferentials.com/ they got me a master kit and ring and pinion for just under $400 on the dot i went with 3.71 gears and have liked them so far you can pick up used cone type slips for a good price now and then and if you can rebuild the drop out your self there is a good chance you can hit that $500 dollar mark i had a shop do mine and was only charged $100 for labor