If you are interested in a very good large scale 3D Printer kit, I highly recommend the TronXY X5S. You can currently buy it at GearBest for just $282.
I'm a big fan of CoreXY printers, having build my own highly customized C-Bot about a year ago. CoreXY machines have very low moving mass and can print plastics that extrude easily at high speeds with little to no artifacts. They are almost as good as a Delta printer for speed, but without the Delta printer calibration headaches.
The only real upgrade that I believe the TronXY needs is a 24 volt power supply to replace the 12v one that comes with it. The heatbed is simply not powerful enough on 12 volts. A suitable 24 volt supply can be purchased for around $30.