Call a concrete company they can tell you instantly.
Depends on size and thickness. You take length x Width x Thickness= Then Divide by 27. That will give you How many yards of concrete you need. Then you need to call your local concrete company and...
Here is an estimate from another site. http://en.allexperts.com/q/Building-Homes-Extensions-2333/slab-foundation.htm
Cost would be a factor of size, variety, location, and desired finish.
BETWEEN 3AND5 DOLLARS EACH
About 5 dollars.