Start here: https://www.raspberrypi.com/products/raspberry-pi-4-model-b/
Is it expensive ...
Like everything affected by the headlong lurch into "AI" prices have increased substantially. They now go for about $35.
... and can the average shmuck, like myself, implement this successfully?
The Raspberry Pi is designed for anyone to use, just like a Mac. It requires no specialized programming skills, and setting it up is menu-driven and self-explanatory. Just like a Mac. You have to add a USB-C power supply, SD card, monitor, keyboard, and mouse. Any generic inexpensive components will suffice and there are many options. You might want to install it in a case depending on where it's going to be used. Those components add to the cost, eventually bringing it to that of an inexpensive Brother AirPrint laser printer, but that is the reason for my caveat "if you are motivated beyond reason to keep that printer in service".
If you are averse to littering landfills with perfectly good but outdated printers then a Raspberry Pi is the solution.
Furthermore, out of the box, a standalone Raspberry Pi does everything most people expect of a desktop PC. It runs the latest browsers, email, productivity software, etc, but that's getting far afield from the question at hand.
Read the links in the above, watch the videos, and see for yourself.