try craiglist.org or ebay. You can get a 400 watt hps at High Tech Garden Supply for 137.00 including shipping, that's about as cheap as I've seen one. You could always do a cfl grow.
man i saw some HPS and metal halide bulbs at lowes but the i couldnt get a sales rep to help me find out about a ballast or any shit like that but i think you can get the whole setup there.