Hi Barry, Ignacio:
You will be able to order the PCBs directly from OSH Park for very fair prices, always in batches of 3.
Three (!) PCBs will be USD 2.30 including (!) postage to Europe.
As for the parts, I will set up a Mouser part list, so you can order there directly. Due to minimal order constraints and surcharges, this makes more sense for quantities of 10 or greater, but any club or group could handle that locally (it does not sense for me to order the parts in 100s and then have the logistics to set up billing etc. for individual parts). Also, in Germany it is pretty much complicated to sell electronic kits due to legal and regulatory constraints - doable, but no business you would start for small stuff.
So this will be really open hardware and all files and documentation will be on the Web on Github.
As for the trimmer, this is the only critical component, because the footprints of SMD trimpots vary a lot. I am still searching for a popular brand and will include that in the updated PCB design.
If you build a THT version with wiring by your own, you can use any trimpot you like. Just keep in mind to keep the directional coupler part as symmetrical as possible.
If you have a bit more time, then I would advise you to wait for my digital version, which will be more accurate and not more expensive.