If only I'd done a little more research, I might have known that Donald Judd did, in fact, make a smaller version of his daybed. This almost-twin-sized version [111x116x204cm] dated from 1993, while the artist was still alive, was fabricated, like all Judd's wooden furniture, by Jeff Jamieson.
It's being auctioned at Phillips on Thursday, but you can also bid along on eBay Live. It's Texas Pine [not fir, as the eBay description says], the least expensive wood the Daybed comes in [the double-sized is/was $18K with a Judd Estate stamp]. But furniture made during Judd's lifetime is worth more. Yet a smaller, one-off piece could be cheaper. Or rarer and hence more expensive. Or--whatever. If you're in the market for a Judd twin bed, you're looking at an opening bid of $22,000 and an estimate of $35-45,000. A full-sized Judd-stamped bed sold for $70,000 at Sotheby's a few months ago. Good luck!
[update: ouch, it sold for $65K, plus commission =$78,000. Back to the drawing board...]
Donald Judd Daybed, est $35-45,000, auction Dec. 14 [ebay.com via andy]