Any system capable of running OpenWRT. https://openwrt.org/supported_devices You might find / inquire about specific devices at the OpenWRT subreddit: https://old.reddit.com/r/openwrt/ The Turris Omnia is priced above your preferred range, but is effectively a small server and has excellent capabilities. It runs a specifically-tuned and live-upgradable version of OpenWRT: https://www.turris.com/en/omnia/overview/
IMHO, skip OpenWRT. It is much more difficult to get working correctly than HN likes to admit. There’s a non-trivial chance you will spend hours and hours reflashing your router and reading forum posts until you eventually brick it. It’s just like Raspberry Pis. Theoretically the right choice but practically speaking a huge time sink and poor, unstable experience that is best left to hobbiest tinkering or networking…
It's cloud-free, spyware-free, adware-free.
The default configuration works with the same basic configuration any consumer-grade system would require.
Extensive configuration capability is offered through either of two graphical front-ends, the basic Turris, the advanced Luci, or for those who prefer talking in words rather than gestures, a highly capable Linux system residing underneath.