OUCH! Seeing that stepnose grille on the pavement is painful. Unless the thing is broken beyond all repair, I would focus on removing and preserving that. It's probably worth more than the differential.
Value for your diff? Is it a 4.56? How are the disks and calipers? 4.56's are pretty common, so if you can get someone to show up and collect it (rather than ask you to ship it to Timbuktu) any reasonable number should be acceptable. If it is a 4.10, 5.12, or the mythical 4.30, its value would be greater.
Is the "T" arm included, and if so, how are its outer bushings? A "T" arm with sound bushings has some value, as it is a bit of a job to replace the bushings.
You can ship it via UPS or FedEx if you take it apart. Remove the brakes and axles, then separate the pumpkin from the axle tube. The pumpkin side with the gears is the important part of the assembly. You can carefully count the gear teeth through the drain hole to figure out the ratio but I forget the numbers. RJ might know.