diy cnc engraving machine fair price?

Have been looking for a newbie starter -machine of some sort. Someone locally asked me to put in a price for his project, which looks a bit like this (no it isn't this one):

http://hackedgadgets.com/wp-content/_finished_cnc.jpg

- except made of aluminium -profile (not solid material).
- Travels some 12" x 10" x 3.5"
- Each axis has got ball screws
- Stepper motors
- Board included

* Excluded items (I would have to buy myself, elsewhere):
- power supply 48V
- Kress drill/grinder

So apart from these, it would be a working setup.

Please how much would be a fair price
a) for a buyer?
b) for a seller?
c) rough cost of parts? (or do I need to ask further questions, to answer this?)

I kind of would like to take a deep dive, and build my own from scratch, but not sure if I am ready for it yet. (if you can think of some relatively straightforward kit or project, please suggest).

Any views welcome

Cheers for a great forum