Designing a DIY milling / routing / engraving machine

Electronics
I'm in the process of designing a new CNC milling machine (gantry-style) After searching the internet for open-source designs, I couldn't find a design that meet my requirements Below 3000$ cdn At least 36" x 24" work area Extremely rigid frame Must be able to work with wood, plastic, aluminium and steel > 6" clearance on the Z axis  Long lasting mechanic (no plastic wheels to wear down) Open source so I can tweak and upgrade Readily available hardware I've found many designs on http://www.openbuilds.com/?category=cnc-router-builds&id=286 and https://id2cnc.com/ but nothing that meet all my requirements.  I decided that the risk of building a machine that wasn't strong enough and would need  to be replaced in a year outweighted the complexity of a new