How would I, or how much would it cost, to remove this stone pond?
This is called a grotto, it's essentially a shrine to the Virgin Mary.  Since it is not a structure designed to support anything more than the rocks and contain the water, the concrete is most likely just an inche or two thick and easily busted up with a sledge hammer.

The statue has value to a Catholic, you might want to put an add in Craig's List and offer the rocks and statue free to anyone for busting it up and hauling it away.