There are a lot of phones in that range and not all phones are same so its tough to recommend
Xiaomi got new policy, and that is unlocking bootloader now takes 720 hours so vendors dont replace it with fake rom and fake UBL and then sell it
Some phones have anti rollback protection
Which means you cant downgrade to certain level unless you make small modification, but there are few topics for every phone which removes ARB trigger script
I own redmi note 5 ai, device is awesome
And yes my phone did came with anti 4
But it doesnt stop me from flashing roms onto it, its quite easy, just need extra few steps
I have the same problem, I have a 2016 model I believe. I have installed Cyanogen Mod 12.1 (5.1) and Windows 10, but I don't have TWRP installed. I can't remember how I did it though! I want to install the Lineage android now. I have tried turning on usb debugging and oem unlocking in Cyanogen but I never get a request screen come up for usb debugging permission. I have the Intel drivers installed but as far as I can see it's not showing a connection to the Hi10 Pro. I am using 1803 Win 10 x64, wonder if that has something to do with it. I tried putting it in fastboot mode and flashing but it just says waiting for device or something and nothing happens.
Check Kimovil for specs and prices.
I can't remember what the best Xiaomi phone in the €120 range is but there's definitely something at that price point.
Note that on most or all Xiaomi phones the bootloader is unlocked but can be unlocked officially by using the Xiaomi tool and instructions.
So generally you can install TWRP, root and install a custom ROM if you prefer that to MIUI.
I liked MIUI for a long time but now I find that it contains too much bloat/crap/adware so I'm moving back towards LineageOS.
I installed LineageOS on my son's new Redmi Note 5 recently.
Note that some Xiaomi (and other?) phones may have ARB (https://www.xda-developers.com/xiaomi-anti-rollback-protection-brick-phone/) so you want to avoid such an update if you want freedom to install certain ROMs.
Hope this helps.