You could run it on a ATX PSU, which you can get for free many places. The cheapest chinese driver board is around 45$ and steppers can be found at 30$. The bearings can be found at the price of 25$ for 50pcs. Then there is threaded rod, tuping, MDF, nuts, bolts and a dremel. My guess would be everything in between 250 and 450 depending on how lucky you are with getting the parts cheap.
Here in Denmark things are quite pricy and there is a lot of tax when importing things from outside the European Union. So i would have to pay around 400$ for these parts.