What bandwidth do you expect to need?
"Mid-range" all-in-one routers (ath79) are, from my testing, only capable of around 10-15 Mbps OpenVPN throughput. If WireGuard meets your security, robustness, and other requirements, that class of router seems capable of around 3x that throughput.
A Raspberry Pi might be a reasonable, inexpensive VPN end point, though I haven't tested their throughput at all.
While I don't have one in my hands yet, the Marvell-based https://www.gl-inet.com/products/gl-mv1000/ might be a mid-priced option of interest as well. GL.iNet's reporting of VPN throughput has been "honest", in my opinion. Their materials state 97 Mbps as an OpenVPN client, with a reasonable warning that performance as a server will be less. I would guess that something around 50 Mbps would be possible. I would not consider the EspressoBin v7, due to reports of thermal design issues (see Amazon US reviews, or https://forum.armbian.com/topic/10429-how-to-make-espressobin-v7-stable/ as examples of third-party reports).
An x86_64/AMD64 VM is another option, perhaps at "no financial cost".