I recently bought a UZ801 USB Wifi 4G dongle for 10€ incl shipping from China and flashed linux onto it. It's a full-on router running OpenWRT in my workshop now. Can definitely recommend tinkering with such boards, I'm having a lot of fun, especially because of the limitations (384MB RAM, 2GB flash). A lot of tools I wanted on there I had to reimplement in Rust to be more resource-efficient.

You can raise the ram limit by disabling the modem as it turns out! It uses the same ram as the rest of the SOC so turning it off gets you that back.