I think it is hard to find an 8.8 or ford9" that is a simple "bolt on" for most of us.
You've obviously never loooked then. OK4wd out of NY offers a bolt in Ford 8.8 axle, set up with TJ or YJ bracketry, 4.10 gears, disc brakes, and a limited slip, that's a complete bolt-in for less than $1500 ($1100 for YJ).
http://www.ok4wd.com/product.asp?id=547Not to mention Currie Enterprises, who will build you a complete bolt in 9" as well. Hell, if you've got a TJ, head to the junkyard or ebay and find yourself a D44 rear, and you're done!!!
Every 4wd shop, with the exception of national retail chains should also be able to do the custom axle setup work for you. Just call around and check.