How much does one of these usually sell for?
The question should be not what they sell for but what they are worth? Think of supply and demand. You have 10. The demand is zero. That means there is no equilibrium price where supply equals demand. Sell them for scrap and reclaim your air space.
A quick search shows various amounts
How many people buy used parts to install in a Genset ?
Although it was secondhand, it had never been installed on any machine. The previous owner had run a business poorly, and large engines required this type of flexible gear coupling to protect them.
So these are N.O.S. New Old Stock Not "Take offs" If you have them in the OEM packaging, would help sell them much better.
Look up the new cost through your CAT dealer and throw it up on eBay for 50-70% OBO. Used and NOS generator parts are sold all the time on there to avoid smaller outfits paying for dealer techs and pricing.