The question cannot be answered as asked, since building a robot is such a vague description. The definition of a robot can be anything from an automated arm that pushes something when a proximity sensor fires, all the way to something unimaginably complex.
As such, the cost can be anything from just a few dollars, up to the costs of whatever hardware you want to put in it.
10,000
50.00
a lot
The only robots that have been in space are called rovers. It costs NASA about 2.5 billion dollars to build them.
too much
The ISBN of How to Build a Robot Army is 1596912812.
The question is similar to asking, "how much does an automobile cost?" A robot's cost is determined by functionality. As you put in place more sensors, actuators and additional power, the price increases.
The lower the cost to buy or build the lower the quality of what you get for the money
At the time of this posting in August 2012 the NAO Robot lists for $16,999 for a single unit.
How to Build a Robot Army has 176 pages.
Well there is no specific cost it depends what you build it out of
90 cents