Has anyone upgraded their 4x2 to 4x4 and gotten an approximate cost. I imagine the VFD/Spindle/Controls remain the same. I know linear rails, frame work and rack need to be replaced/extended. Wondering if they replace the entire rail and longitudinal rack or they just extend the 80/20 frame ?

Just trying to get a ballpark estimate as I am considering starting with a 4x2 and extending it as I get space. Thanks