Not really sure what adapter you're talking about man, but all I know is, is that you NEED to get a ballast that is rated to handle the HPS bulb. The ballast itself is just a certain kind of transformer as well as a capacitor which helps jump the power for a bit to start the bulb. Trying to rig something else would definitly be dangerous! There are metal halide bulbs that come with some kind of adaptation where you can screw the metal halide bulb into the high pressure sodium ballast. That's all I can tell you about an adapter because I'm pretty sure what ever you're thinking of will NOT work. With that kind of budget ($50), the only thing that will work for you are CFL's. And to get the same amount of lumens per square feet you are probably not gonna do it for $50.