I’ve got these motor mounts from rattmmotor88 ebay seller for just $15.67 each one, shipping and hex screws included. Shipping was really fast (fedex), just eight days (I use to wait 30 to 50 days for items from china).
Packaging could be better; there are some scratches, but nothing you can’t fix with a file. Internal milling is great. External sanding finishing looks nice, but flatness is somewhat compromised; milling finishing for mounting surfaces would have been great. I don’t understand why they make motor recess 42mm diameter when it should be 38mm; anyway this is not a serious issue. Of course a critical parameter in these mounts is the space they add between motor and mount surface; 40mm in this case.
As this kind of mount allows a lot of play between leadscrew axis and motor axis, you should be careful every time you install X or Y motors, especially if you’ve got heavy motors and/or your couplings are “flexible type”.