I found some 4.10's at mustangtuner.com for $132.99, free shipping, but are not Ford Racing. They're Motive Performance Plus. Anyone ever heard of them?
Keep your eyes open, your ears cleaned out, and search. I have a list of things I want to do all the time. When I can find a deal, I go for it. Knowing people who are a step or few ahead of you is great because you can get great hand-me-downs from faster foxbodies.