Xiaomi - Xiaomi WR30U

Running 4 of these in different locations for more than a year now without any glitches. A very capable model with Wifi6, 4 gigabit ports, 256RAM and 2 ARM cores. But beware of different revisions -- the most recent one (RD03v2) is not supported, since it's Qualcomm hardware instead of MediaTek

Based on your requirements, Xiaomi AX3000T is your best choice and it's only $32 in my country.

I am using Mi Router 4 and Mi WR30U myself. Both are cheap but the WR30U has worse documentation for being less popular.  If you are only looking for a small upgrade without going extra, Mi Router 4 (not 4a) has 128MB flash, mainline OpenWRT support and decent documentation. It can be found for a little as ~$7USD second hand so it will fit in your budget even if you spend all of it importing 

Not 6GHz but will serve your purpose Mi WR30U or Mi AX3000T you can get on taobao for around $17 USD each if you buy in bulk. Four Ethernet ports and stable WiFi 6 on a low power draw. The price allows you to double your number of APs if you want more coverage You got downvoted because you used the word router to refer to the hardware when people are asking for what role you'd use the device as. You really only need one router (role) with many switches and APs(role). Whereas how you achieve it by flashing OpenWRT on consumer grade router (hardware that can do routing, switching and AP).

There are quite a lot of options, I have redmi ax6000(mt7986), Xiaomi wr30u, Cudy tr3000. Not new devices, but it’s cheap and also powerful devices.

Xiaomi AX3000T - has 5GHz 160Hz which will be more than enough for your speed requirements. Great processor, ample ROM space and RAM.