Wow! Those are expensive. I get mine from Global Tooling and Supply at about half that of AZ Carbide.I’ve used the diamond card along with cutting fluid to sharpen my carbide tools with mixed results. What I’ve found works best is just buy new inserts. I know this can be pricey but I’ve found AZ Carbides has some pretty good prices and ship quickly.
The other thing I’ve noticed are the inserts I get from AZ Carbides seem to be a little sharper than others purchased. May or may not be true, it just seems like it to me.