It's a little rough, and has had a tailgate cut into it, but it's solid. $500 would be a fair price, but shoot for lower, offer $3-$350 and go from there.
It's complete, with the lunette and parking brake handle, only missing the original tail lights. That's no big deal, as even when converted to 12V bulbs, they aren't very bright.
I would go for it, these trailers are getting harder to find. It needs some work, but will be worth it.
I have an RTT mounted on mine, and love it! My dad left his 'stock' and loves it, we use both trailers a lot.
BTW: if you get it, and would like to part with the lunette (ring part of the hitch) I'd be willing to buy it! (and swap you my tongue to boot!)
Mine was cut off, and had a 2" ball style hitch welded to it.