Cost would be a factor of size, variety, location, and desired finish.
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...
you should check the grand exchange database for the current price
Here is an estimate from another site. http://en.allexperts.com/q/Building-Homes-Extensions-2333/slab-foundation.htm
Over $400
Market Price is currently at: 268.2k.