I needed a RH side mirror for my 69. It was the ribbed unit made By Goodmark and sold through the parts geek for $14.95 + shipping. Got it and I wasn't disappointed, it was just off from what my NOS unit was I was replacing.
The Goodmark unit had the rib exactly like my NOS unit, it was a little too wide at the end. Besides that, nothing else looked bad.
For the price it's ok.....or you can pay through the nose buying one from Heartbeat City.
But as mentioned before some of the NOS ones you see on eBay are in worse condition than the repros. Today most NOS units are usually returns that were reconstituted back into the parts stream by unsatisfied buyers.