To date I have designed three version of the Keyboard Development Module, each having slight updates.

The first provided four test RGB leds and used a 30 pin connector and a three pin connector for the RGB, the second removed the RGB leds, simplified the Boot, Reset switches and changed to a single 34 pin 1.27mm connector.

The third and last version, is identical to the second but changes the position of the connector making connection to the basic keyboard easier and more natural.

All three modules work perfectly for developing and testing QMK/VIA code but once you are finished your code development, I want to be able to use them on the actual keyboard. To this end I provide several basis keyboards containing all the necessary parts allowing connection to one of the modules.

Note, I've only tested the first two modules as the final design has not yet arrived but as it only relocates the connector I don't see any problems.

The final version pictured below.

It appears to be more cost effective to use a module as opposed to building a keyboard including the full electronics from the beginning. 

You can hand assemble the keyboard as all components are pretty easy to hand solder and getting the modules fully assembled is cost effective, less than €20 and the keyboard is about €10. The FR4 Plate cost about €5 (all prices are less shipping).

Note, I used both JLCPCB (Keyboard & Plate) and PCB Way (Assembled Modules) as they offer better prices depending on size, assembled etc...

With a full 3d printed case, the full cost for a keyboard should be less than €45, mind you, you have to purchase a minimum of five boards and pay for shipping... ideally you could get five friends to join in.