Minimum order quantity for the populated board is 2. That costs, iirc, around €20 for both plus shipping (if you are patient, that’s a few more €).

This micro soldering part can by now be ordered to be included in the assembly, so that you don’t have to solder it. I haven’t tried the process of ordering extended parts from JLCPCB, but if that works, that’s another ~€10. Otherwise you’ll have to source it yourself and end up with a similar price.

The Blackberry keyboards go for €3-6 on Aliexpress.

A 5-pack of the USB connectors is about €10 on Amazon, but on Ali you can get one for ~€1.

That’s all the electronics, so for two of them, that’s about €40-50.

You also need a 3D print, which costs around €1 if you print it yourself or get a friend to do it. If you order it, that can be anything from €10 to €50. The cost of these services varies wildly.