According to Peter Kitchingman, Canon made a bit over 5,000 of these lenses. Maybe not rare, but definitely uncommon. As for value, I haven’t seen any for sale recently, but it seems they go for about $500.00 USD in good shape. Maybe somebody else can add more.
They were not that common at camera shows and on used gear shelves in photo stores even two decades ago. I only saw two for sale back then ( one which I bought and appears on my avatar) and they were not inexpensive by the standard of that time .
Certain Canon RF lenses like the one you are inquiring about and the 25mm Canon and the 19mm RF Canon lens were known to be hard to find for sale and the price was never a bargain.
I also did manage to find and buy the 25mm lens but the 19mm RF coupled
Canon lens I let pass through my hands when I located one, as I felt it was a focal length that I would rarely use when I thought things over.
Well spotted. It's true I only 'use' one camera one lens one film. I bought this lens from a dealer a while back and used it for a while then put it in my camera drawer. Time to sell it to fund lots and lots of film. Got some more stuff sitting around which needs to go soon too, but difficult to let go.