Since choosing a KB is personal choice, it is impossible to tell which one to go for. Especially regarding mechanical KBs, since they have different switch types to choose from, with vastly different feel, articulation force (e.g how hard you need to press the keys) and there are also tactile switches (tactile bump during key press) and also loud "click" switches.
All that is doable and from the top of my mind, mechanical KBs with USB passthrough, are:
Corsair Strafe RGB
Corsair Strafe RGB Mk.II
Corsair K100 RGB
All 3x KBs i also have. Mk.II is my missus'es KB while K100 is the upgrade for my Strafe. The two Strafe KB i have, have Cherry MX Silent switches, while the K100 has Corsair OPX (optical-mechanical) switches.
While all these KBs do offer solid build quality, plethora of software customization via Corsair iCUE software, per key RGB lighting and also USB passthrough, they also cost A LOT.
Price wise, i payed:
€178 for my Strafe in 2017.
€184 for my Strafe Mk.II in 2019.
€316 for my K100 in 2023.
Corsair Strafe and Strafe Mk.II are EOL as of now. But if you can find one sale somewhere, great. While K100 is way out of your budget + then some. K100 is flagship KB from Corsair as of right now.
But if you end up with Corsair KB, then their mice selection is also good. I also have used several different Corsair mice over the years, while as of right now, i'm using Corsair Nightsword RGB (
specs) alongside other Corsair peripherals (e.g headset).
Looks like you've greatly underestimated what good, mechanical KB costs. Especially if you want software control and USB passthrough.
At your current budget, essentially only option is Endorfy Thock TLK Blue,
specs:
https://endorfy.com/en/product/thock-tkl-blue/
amazon:
https://www.amazon.de/dp/B0BHDST4WY
It isn't full-sized KB. It doesn't have USB passthrough. But it is mechanical with some software control and RGB. Key switch type is Kalih Blue, so it will "click" loudly.
For other options, well, all others are way out of your budget,
pcpp:
https://de.pcpartpicker.com/products/keyboard/#k=1&t=1&sort=price&b=46&n=0
My best advice; go to any PC hardware store and actually test out the display models offered, to get the feel of different key switch types.
E.g on paper, Cherry MX Brown sounded nice to me, but on the spot, trying it out, i didn't like it at all. Instead, Cherry MX Red had the best feel for my preferences.
Or buy the key switch tester, to try many of them out,
amazon de:
https://www.amazon.de/-/en/CHERRY-MX-EXPERIENCE-BOX-Mechanical/dp/B0CC2WZLQ3/
Once you've found out what type of mechanical switch you do like, then you can start researching KBs that have that switch type.
I actually doesn't advise to buy the Endorfy at €55. I think you'd be disappointed in it quite a bit. Blue key switch types are very loud and only few people like them, mostly writers/typists. But for gamers, that loud clicking gets annoying - fast. For you and for everyone around you.
Good brands regarding KB and mice, are Corsair and Logitech. But i'd avoid Razer completely, since Razer hardware is plagued by all sorts of issues.