You can try rolled flashing from a Home Depot store,although the reflective quailities aren't that good.As for a mogul socket,Marine Depot has a good price even with the shipping.It was better than local electrical supply stores.
I've never tried this, but maybe you could get some silver sheet metal & polish it, using metal polish - it might make it sufficiently shiny, though not as shiny as the LFS reflectors.
I used a 24" round metal air duct. They are unrolled when you purchase them and you can use tin snips to cut down to the size you want.
I used this mainly to dissipate heat more than a reflector (my tank is only 18" deep w/ a 250w MH). But, the reflecting qualities are there. Just not as much as stainless or polished aluminum. It is easily "rolled" or bent to fit your needs and attaches easily with self-tapping sheet metal screws. The best part is that it was about $2 at HD. Look in the air/heating aisle.
Im not paying all that monies for a hunk of metal.......anyone have any sugestions for a reflector? I will be spending my money on a do it yourseft balist and a mogel socket but not from a lsf or website.....they must be high......asking that kind of monies