I would honestly recommend buying an old laptop with a broken screen (or an old netbook or something, make sure it has an Ethernet port), a decent DSL modem, a USB network adapter, and a switch if you need it. Now you’ve got everything you need to make a super capable router. Install a very basic Linux distribution and get NAT setup (it’s like 4 or 5 commands), configure the firewall, and your VPN software of choice. I’ve run a setup like this for years and it’s great, because any time a component is “out-of-date” you just update that component. For example, you need AX WiFi instead of AC, just upgrade the WiFi adapter).
I first saw this joke in this demo: https://www.pouet.net/prod.php?which=56549