BIG SIZE + Low Budget + reasonable precision + light tool loads = Garage Door Rail (It is Screws and Slides in one piece)
Just a consideration for you, the Screw driven Garage door Rails combine the screw and track in a single piece. You could get and try out for a very cheap price at garage sales/the Sally's/Op Shops etc. I've noted by push and pull they can be reasonable in terms of repeatability. An added feature -- the screw is supported in the track inside a nylon tube. You'd need to keep the weights down on the gantry or stiffen the setup with some other bits. I've been considering such a design and build -- but this season is soon coming to a close for me and it'll have to wait for next trip.
May seem off the wall - but you asked for ideas. (PUN INTENDED )