Got to thinking for $600 I hope is for a "set" as in both axles. Even at $300 per axle seems kind of spendy to me. My 9" rear was already under my CJ6 I bought for $850, my Wagoneer axle I bought a rusty shell (no interior, motor, trans, or transfer case) for $300 pulled the axle and steering box out. Hope to get at least $200 back out of what is left at the scrapers. When buying axles like this take into account unless you get real lucky and find one the width you need,with limited slip or locker, and in the ratio you want, you are going to have at least $1,000 more in each axle to get it to where you want it. More if you cannot set it up properly and have a professional do it. Even more if you do it yourself and do it wrong!
If you want a 9" Ford for the rear look on Craig's List, find a parts 1/2 ton truck or Bronco for cheap and pull the parts you need. If there is anything else good you can resell to make it even cheaper. This was not the case with my Wagoneer but, got it cheap enough not to worry too much about it.
I own a Harley and a JEEP, still some people can't figure out why I'm broke!