And, of course, it depends on the size of the enclosure, and how far away the animals would be. Light intensity follows the inverse square law- if the intensity at 1m is 100, at 2m it will be 25, 3m- 11.1, 4m- 6.25, etc. I doubt many people have enclosures large enough to be suitable for HPS lights.
Cheapest place to get them, though, would be police auctions. Apparently some people do use them for things other than tomatoes:-) and get caught. Last auction I was at, they practically gave away a whole skid of HPS ballasts, fixtures, reflectors & bulbs. I've always wondered if they note the name and address of the person who buys them for future reference:-)