Cost effective would definitely be an 8.8 Explore or Mountaineer
gear selection available 3.55,3.73,4.10
Locker already installed not the best but will work and can easily be upgraded
Leaf spring pads are very close to the proper spacing
Availability is PLENTIFUL
The only drawback is needing to use 4th Gen f body or Corvette backspacing, you can use mustang rear wheels or you can have the axles and rotors redrilled to GM pattern
For the money, you can't beat it. They are very plentiful here in Houston, and cost about $200 complete. Catch a 1/2 off day, and hello...$100. My 8.8 (which is fully built) puts up with 800HP, but put up with 650 until I rebuilt it, and added more power. There are options here - you can pull an extra short-side axle, and then narrow the long-side axle tube, then install the extra short-side axle, and you will be good to go with normal backspacing on your Ford 5x5 wheels, or you can have the axles drilled with the chevy 5x4.75 pattern. By narrowing the rear, you will also have a "centered" pumkin. The 8.8 is 35 lbs lighter than a 9in.