69/70 NOS rear bumpers are sought after because Most (all) repros are too wide .... I'd pay 500.00 for it but you could probably get more. The bad part is that unless it's a really old NOS part, the Chrome can be pretty bad (grinder marks, ect), and the dates pretty visible so they don't appeal to the "date correct" crowd. I used NOS bumpers from the late 80's on one of my CJ's and had them rechromed.
Keep looking on Ebay, they show up time to time...
Hope this helps, John