Google "The Halloween Adventure Store." They have a web site and sell mail order. I've been racking up on wigs for $15 each. That's a tough price to beat. They do sell tombstones too.
To cut the styrofoam (lots of toxic smoke -- outdoors please), we used a soldering gun with replaceable tips and used heavy guage uncoated/untreated wire formed into a longer blade shape.
Gray latex house paint as a base layer (spray paint melts styrofoam), then some character added using black spritzed from a distance, then some blues and greens to look a bit mossy (you won't see how cool they look in the B/W pic attached, but they looked cool in color!).
They are held in the ground using bamboo skewers/chopsticks.