Whats is worth 8 3/4 with suregrip, drum to drum, 3.91's

My thoughts is that this rear end would live forever is someones 400-500 HP car...
So I should pass it on while
1. its in great working order
2. it has value to myself as a seller, and to the future buyer

I need to start pricing out what Im going to have in a 9 inch, and go from there.

thanks all, seems I have my ballpark numbers.
I know you're looking to do a 9 in but I will give you a rundown on my D60 if you'd like or not....
I bought a D60 out of Craigslist from a Dodge 3/4 ton truck for $160. I lucked out and it had good 4.10 gears. sold quickly all the brakes and axles and all that which would happen to be in very good condition for 40 bucks. Call Dr diff and ordered $125 spooi $50 bearings and shims, and for $300 Moyer 35 spline axles with green bearings. = $545. Oh yeah also $75 to dr diff for Mopar housing ends to melt the backing plates on. =$620 +$350 for shortening the actual and Welding on the ends and actually welding the tubes to the case for strength. And 175 to set up the gears professionally. I reused all my brakes and backing plates. = $1145. Plus I would say another $55 and shipping fees and gear oil. For a total all in cost of about $1,200.