Not sure where you live. But Wi-Fi routers are often given away for free on Facebook marketplace and buy-nothing groups.
Depending on your level of technical skill, there are other options. If you can get a free really old garbage computer that runs, you could install Linux on that with a firewall and tailscale, and nothing else. Then you connect your phone or laptop to tailscale as a vpn, with that computer as the exit node. Then no matter where you are, your traffic is going through that really secure firewalled Linux computer.