That's a tight budget in terms of things that are programmable.
You could try using one of these with any old TKL you happen to find: USB to USB keyboard converter
Well... As far as I saw in reddit and the Internet, the ISO spanish layout requires a keymap to handle the eur symbol, the bit enter key, the ñ... Or I'm a bit confused and just setting the language to Spanish Spain is enough in Windows/Linux/Mac and it's not necessary to have a TKG keyboard.
For some reason, I was thinking about having to change the language on every single computer you connect it to (without programmability), but you obviously wouldn't have to worry about that with computers that are all in Spain.
And about the tool you linked, sorry, but I don't quite understand the use of it, sorry 
The gist of it is that it acts as an additional external keyboard controller, which you can program, so that everything you connect to it will have the same mapping.
I'm no expert on the LEGO boards, but I don't think that there are many options out there for TKLs vs the more popular, more tiny layouts. You might be best served trying to find a used Cooler Master QuickFire with MX browns, and replace the controller with a programmable one, if you can even still find them: Replacement controllers
I don't know what LEGO means, but assuming it's about making a custom keyboard, I was thinking on getting a Ducky TKL, but there's not in Spain the one I want...
I call the enthusiast kit boards LEGO boards, since you're not really building anything custom (that makes me think of hand wiring, designing PCBs and cases, modifying an existing design, etc), just picking and choosing parts and assembling them. Not that that's bad either, it is wonderful to have options like that available.
You could try this as well: XD87
A Reddit post I found on it seems to suggest that the plastic case for it sucks. Might want to try the stainless one.
Yeah, I was looking for it yesterday. The problem is that I contacted the vendor but they didn't really solve my questions. I can get only the board there and the case in another place, that's not a problem, my real problem is the keyboard layout and the keyset. I can learn how to test the board, how to solder the switches, how to flash with the tool they put in the description (and I know how to solder, that I don't need to learn!).
From KPrepublic? The stainless case is on the same website. I imagine they both ship from China, but maybe not?
Hopefully others will have better ideas.
Thank you for your reply!
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You're welcome.
Is this more a supply thing specific to Spain then? People seem to order a lot of things from China, regardless of where they live.
Did you not want the cap set that you did find?