umm... you can get 75w hps setups at homedepot and lowes
but for they're price (like atleast 60 bucks a pop) for the price 2 you can get the better one online (which sucks if you can't order online)
other than that, a hydro store would be the best place to go, but here in town, the cheapest setup they have for a 400w hps (this one has the built in ballast to the reflector, which i don't want cuz of heat issues) goes for about 180 after taxes and shit.... but you'd still be able to get one for that price
other than that, do lots of reading about them, go to a commercial lighting supply place nearby (look in the yellow pages for them) and usually they have HID setups (i mean, hps and mh lamps fill most streelights across the us, if not the world, lol)
i'm rambling now, hope some of this was help... if not, tell me and i'll try and clarify or help more in whatever way i can
best of luck though!!!