It's hard to buy the first one when this board is only a little more expensive and comes with everything else (even if I don't need the everything else).
If I had circuit design skills and patience, I'd try to whip something up using the 'back to back' PHY mode, in theory, you connect a 10base-T1L PHY up to a 10base-T PHY, setup the proper 'straps', put in the right passive components, supply power, and that's it; no microcontroller required.
https://www.methodedatamate.com/10base-t-to-10base-t1l-media...
But it doesn't look like 'commodity' cheap - it's probably several times the price of the beagle...