Seriously...did you buy it new? If so, what did you pay for it? (You don't have to answer that publicly). One way is to do some research and see if you can find any like yours that have sold recently. Another way would be to look at the prices people pay on Ebay for equipment similar to yours. Just guessing, it would probably sell for somewhere between half and three-quarters of what it sells for new, depending on how many people want/need it at the time you're selling and how badly you want to get rid of it... Scott
The aftermarket ones mentioned that can be purchased for around $300-$350 new are FAR stronger than the original item. If you're into serious abuse, get the aftermarket part. Most offer billet caps and 5/8" fasteners, where the originals have much thinner cast caps and 1/2" bolts. There's no comparison in strength. I would think original units would be worth around $200 bare.
To build a bulletproof unit, you'll want to add an aftermarket pinion support. Unless you are into EXTREME abuse, the Daytona support (available from Ford) uses a much larger bearing than the standard unit, and works great on street/strip cars. It has large oil passages for long life on the street. Many aftermarket units do not, and are dragstrip only. The Daytona support can be had for around $100 or so.
Be sure eliminate the crush sleeve, and set the pinion bearing preload with a solid shim. These kits are less than $20 and use what looks like a short piece of pipe and a handful of shims. These are used in place of the crush sleeve. Trial and error with the shims is used on assembly until the bearing preload is right. After it is set, it won't change. The rear can be abused, and pinion yokes can be changed will without fear of messing up the pinion preload.
I seem to remember the HRW cases selling for $295 thru Scummit for the longes time. The Strange "N" case housings are about $379 but not the HRWs. The caps are weaker than Strange. I considered one but I didn't like the caps so I got a Strange "N" case with FMS Datona pinion support, Strange 31 spline spool, Zoom gears, Moser race axles( not to be used on the street with stiff sidewall street tires but great with slicks), billet yoke, billet straps, and back brace on housing.