I built one in '96 for $20 out of the junk boxes under the tables at computer fairs, everything a buck or two. Was a pine technology VLB board, LIF, 5V only, stuck a DX33 in it, used VLB i/o card, actually the $1 one turned out to be "too good" had 16550 UARTs on, so swapped that for the one in my main rig with the lame 16450s. Think it was a chips and technology ISA VGA card, HDD was shatty, lots of bad sectors partitioned out, and another 3/4 height 3.5 40MB that was slow as molasses. Don't think I bothered with sound. Anyway it was my b!tch box for trying out slackware on and other experiments. Funny thing was, it ran faster than this machine a guy called Jay had, who was in the EE course with a buddy of mine... He spent $200 on this ex "high end CAD workstation" 2nd hand 486, with an original AT type desktop case you normally only see on 286es and a few 386, and it must have been a '91 or something, DX33, EISA motherboard with weird long slot extensions with discrete chip memory expansion boards that gave him 8MB but about 13 wait states because it was so slow, don't think the board had L2 either, 1MB on a VGA card and that thing was full length too to get the MB in 32 or so chips. It also had a weitek co-pro, only one I've ever seen, but pretty useless for anything but autocad. Anyway, he needed 2 levels of border to play doom deathmatch on it and not get killed pretty much instantly.
Seen some short, all ISA boards with a SX soldered on, they can't be all that zippy. There's someone around here with that U5S board, which unfortunately doesn't show off the U5S to great advantage.
There's some big ole VGA cards around full height nearly with 512MB on and 100ns RAM that aren't terribly swift, they'd be pedestrian in a 386 though. Thinking western digital for some reason, think I had one with an edge connector feature connector and 9 and 15 pin outputs.
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.