The coopers are quite a bit more expensive. I emailed them for a quote on a 100w HPS OVZ, 120 volt R-NPF ballast, acrylic lens, PC recep and the cost was around $110.
On ebay i saw "MSRP over $300" on a listing for either a 250 or 400w HPS OVX. That's clearly off thoguh. Not even a GE M-400 costs that and that's one of the most expensive medium sixed fixture on the market. (Hubbels are most likely more). The 125 might cost around 200 dollars or so.....
i doubt $300 bucks is the real price. I did see that on ebay though. Probably to make their price look better. I'd guess a 400w OVX is around $170-190.
And before I got one 95 dollars was the price for the 150 watt 115.