Yes, exactly that, motherboard gouging.
During the past few decades, a lot of PCs ended in landfills, so I can understand complete working branded 286/386/486 PCs are now commanding high prices. Maybe even not so old PCs are now commanding high prices. Still, we are talking about complete or somewhat complete PCs.
But crappy old motherboards? you know, the cheap ones (Biostar, PC Chips, ECS, Soyo, etc) made in the millions, that allowed you to assemble inexpensive desktop PCs about a decade ago.
Take a look at this one for example:
Sometime in 2003 I bought one of these to make a cheap computer, so I know it. This was not state of the art or anything memorable back then, however someone thinks it is some kind of museum highly collectible piece. Go figure.
These things should be free or nominal cost so they don’t end up on a landfill.
CPUs like Socket 370s PIII and Celerons, PC66/100/133 ram chips are also beginning to command high prices. It is just getting ridiculous.