Keychron K8 is my go to recommendation if you are looking for a simple prebuilt mech, and it's cheap too.
Non mx keyboards can be good as well, If you look around on marketplaces (espically japanese marketplaces) you can find great deal on topre keyboards, you would be looking for a realforce tkl, so try and get one around your budget if you want to go that route.
You can also go to Unicomp and buy a mini m keyboard with buckling springs, which feel really nice -
https://www.pckeyboard.com/page/product/MINI_M (I really like buckling springs and would recommend them)
These technically aren't mechanical but most keyboard enthusiasts know how good they feel and lump them in with mx boards.
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