Dumb question, but have you looked on CL? Maybe not for desks, but for materials? I check that out all the time, and every now and then I find a good deal. I find "scrap" wood, but it's large enough I did a new desk not that long ago. Or you could find a POS with that hutch looking thing on the back for cheap and just remove the top. I'm sure even that might give you more room, and you might find one with a keyboard slide if you wanted one.