having build my own CNC from scratch, i wouldnt recommend buying plans for one.
making one often involves adapting the design to the material you can get your hands on.
in my case, i started by purchasing two strong aluminium tubes, which i planed to used as the basis for the gantry. I had very little choice in the dimensions, so the rest followed.
Of course, the design still needs to be planned, but if it is to be a serious machine (not an MDF one) then it is likely to be fully custom made.you cn probably find some posts on here with my machine in (it's 2x1m, and probably i excess of 250Kg)
That's another thing with CNC. you cant half do it. a cheap, inacurate machine will be frustrating to use, and wastefull. you will probably end up taking it apart to sell the bits to try recover your investment.