If you can afford it, I would be tempted to find a used tranny to put in it. It will be worth FAR more money, and you can be sure that anyone who buys it the way it is now, will do exactly that.
Those trucks are too good to go to scrap just yet, unless you have 400,000 miles on it.
A good salvage yard will have a nationwide database to try and find a tranny for your truck, if you choose that route.
As it is now, I would think you could get $1500 for it, but not at a salvage yard.