The lowest I've found at the time of writing is about £32 for 8 motors (before VAT). The reason for this change is because I still haven't gotten a response for the seller of the other motor and, while waiting around for one, I noticed that the connection socket looked longer than usual. That's because it actually is:

These 23mm motors come with their own cable, but since it's Dupont-terminated, I'm likely still going to get XH-terminated cabling. Dupont seems to work fine on the 4-in CR600S though so perhaps I can save £3 and just make sure they're cable-tied in place to remove the risk of a loose connection. Nah. It's £3.

Another benefit is that this motor is much more common, meaning that there's a higher chance of reproducability.

I've designed a 4mm spacer so that the motors can be mounted onto 2020-series 4040 extrusion:

I'm going to see if I can get it laser cut in 4mm acrylic along with the 1mm PTFE.

Surprisingly, the BOM doesn't change all that much at all.