I’m not sure about Euro pricing, but I think you should be pretty close to a Ducky One Two, which comes in a few different layouts and switch options. These are really well regarded in the community and I believe they have a silent option.

Personally, for silent boards I am a really big fan of Topre, but they are going to be a bit above the range you’re looking for. They are also not technically “mechanical”, but it’s splitting hairs.

I have a whole stable of mechanical keyboards, most of which are fairly high end by most peoples’ standards and most of which I have built/lubed/soldered myself so I might be a little too deep in it, but I will say that my daily driver has been a Leopold FC980C Topre board for about the last 3 years and I have never thought about replacing it.

Niz makes some much more affordable electrostatic-capacitive boards that could potentially offer a similar experience to Topre boards within your price range but I haven’t personally used one. Worth a look though.