Any helmet is better than no helmet and an unprotected cranium. Even a construction hardhat. Right now I could choose between a climbing helmet (Petzl), a bicycling helmet, and a construction grade hard hat, courtesy of CERT training. Typical retail costs range from eight dollars (hard hat) to around 100 bucks (climbing helmet). The climbing helmet offers the best protection and will most likely remain on the head after first impact.

The Cert hard hat, my most recent acquisition, came without a chin strap, seriously diminishing its capability. I was glad to find one that works. Now it is actually useful around modest hazards.