If you can find a cheap off lease/used enterprise workstation and get a decent nic that could take your budget down for a router . I was running an optiplex 9010 with a i340-T4 as my opnsense box for years and that was ~75 USD in 2020.
Edit: I ended up picking this little box a year ago for 60 bucks and love it. Way less awkward in the living room than a sff PC as a router.
