Is a cahin driven y axis that is six feet feesable? What is the best setup other than ballscrew?

The main reason why we chose a chain driven CNC machine is to keep cost down, and works perfectly! It is also pretty simple to setup, so in your application it is feesable! We currently have our largest CNC machine (greeBull 6X) which runs roller chain for both the X-axis(12Ft.) and Y-axis(6Ft.). In longer lengths the Lead Screw, and Ball Screw will be hard to get in those lengths without any bends or having it perfectly straight at a low cost, and maybe be harder to accomplish. Most larger CNC machines, will have to use rack and pinion for the larger lengths, which will have a more complex assembly. Both the ball screw and rack and pinion will both run (mostly) on aluminum machines.