I've seen cheap 2' (or was it 18") stake in a box.
Alternately, I'd suggest just using contractor marking spray paint. You can get it in neon green to contrast with the grass, yet be different from the orange (data), red (power), blue (water), and yellow (gas) used by the line locators. A 10' piece of PVC makes a great strait edge, and you can stretch the paint using dashed lines.