Tin, I have been beavering away with research too. I think I will go the DIY way if it becomes reality as the fun for me might be in making the machine! The Ordbot Hadron is a very interesting open source design that is high quality. This is just the frame and steppers and will be cheaper on your side of the world.
It is made of Makerslide which is a cool open source extrusion that is designed for making 3D printers. There are a lot of accessories available to bolt it all together. 3D drawings are available.
Feedback from guys with CNC and cheap printers is getting the Z axis working well with two steppers is problematic as the steppers can get out of sync. So If I build one, it will be no holes barred.
So my current thinking For the Z is to use linear slides to move the bed up and down and a single 1202 Ball slide (12mm shaft, 2mm pitch) driven by a 400 step (0.9deg) stepper. This will give 5 micron accuracy without microstepping. If the ball screw is centred on one side of the build platform, a couple of rods and linear bearings might be added on the opposite two corners.
I thought the X axis would be attached to the Z axis platform and the Y axis suspended from above.
I was trying to avoid using belts as keeping them tight to eliminate backlash is problematic but it seems that ball screws are a bit to slow on the X & Y axes. The other fast technology is to use a gear rack on the axis with a cog on the stepper as per the longitudinal drive on a lathe. I just don't know how much backlash this might add to the system or how to control it.
The RUMBA board supports up to three extruders and the configuration shown has a newer stepper board that runs cooler (which I know is problematic from playing with the 4988 driver board)
I was gong to use the opensource Bulldog XL extruder using a bowden setup that moves the heavy stepper assembly off the moving platform for speed (eg Bowden cable is like the throttle cable on a lawn mower)
Once configured with the hot ends, this extruder path is quite pricey at around $250 each and I was up for around $1k for a single extruder model with roughly a 12" (305mm) cube as a build area.
Because I have a relationship with a laser cutter, I thought the frame would be cut from 2mm or 3mm steel plate. This would allow precise positioning of mounting holes plus add a bit of weight which has to help accuracy.
Hope that helps (or confuses)