A quick search found a few immediately. Example

Note that they still need to be plugged into an outlet to get enough power to run, so it might not help given that you said it isn't near an outlet for powerline.

Your guide looks really complicated and I'm not sure why all of those steps were required for you to get online.

You could have probably just bought a simple IOGEAR adapter like this one: https://www.amazon.com/IOGEAR-Ethernet-2-WiFi-Universal-Wireless-GWU637/dp/B018YPWORE

Just plug it into your PC to configure which Wi-Fi network it connects to or use the WPS button then, after configuring the adapter, you just plug in a network cable from the Dreamcast to the adapter. (Remembering to plug the adapter into the wall or a surge protector for power.)

That should be it.

IOGEAR Ethernet-2-WiFi Universal Wireless Adapter, GWU637,Black https://www.amazon.com/dp/B018YPWORE/ref=cm_sw_r_cp_api_i_PPANW9D3SQ84DNEPSMAH?_encoding=UTF8&psc=1