Don't fall for that, I know I am in country here in Jefferson, but I just had eight yards, formed lightly graded with shovels and pic for $2500. That is 18 x tapered of 50 ft with turn around for Kubota.
When you do the math, that ran @benjamin $312.50 per yard, and he has flat, easily accessible space, based on his photos. So, while the price of concrete alone is cheap, it does add up quickly. The_ Brit_in_ATL ... your drawing appears to show some piers/pads, plus possibly some gravel fill, and even a reference to what appears to be trees, all of which continues to add to the total cost. Yes, $5k for just concrete is high, while $5k for a turn-key landscaped solution may not be.