There are a lot of them, but depending on which features you need and where you live, it might be difficult to get one.
Take a look e.g. at OpenWrt's list of devices "Ideal for OpenWrt": https://openwrt.org/toh/views/toh_available_864
Consider TP-Link Archer C7, for instance. It is an older one, but has reasonably fast hardware, supports IEEE 802.11ac and is available on Amazon. New costs ~75 USD, a "certified refurbished" version costs ~50 USD.