I have built and am currently using an MDF machine built, more or less, to the JGRO design. Plenty of info if you do a Google search. Pro - materials to build are cheap. I went up a size on steel guide tubes, but it still uses skate bearings and threaded rod so didn't cost an arm and a leg. I did spring for bigger motors than recommended and reasonable drive electronics so that I could reuse these later. Fairly simple to build with ordinary tools, although I also used my lathe, milling machine, and 3D printer to produce parts (home-made motor couplings, anti-backlash delrin nuts, etc). Cons - it warps like nobody's business, and it's really, really difficult to keep the bearings in adjustment. Use of M10 threaded rod as a leadscrew may be cheap but the critical speed is low, so my maximum rapid speed is only 900mm/min.

I've done some useful work with it; I was using it today to make drilling jigs for some MDF furniture I'm building (the cutting area is too small to directly CNC cut the cabinet panels) and it's fine for that kind of thing. I've learnt an enormous amount from it (including a long list of what not to do!) at not a very great cost and had a CNC router available for use while planning the Mk2, which is now being built. I wouldn't stop someone building a wooden machine, and I'm sure that you could build something stronger than mine, but just keep in mind that it is going to have limitations and go into it with your eyes open.