As for HID lights you can veg and flower with HPS. Although you will want to use lower intensity light (floro/CFL) when germinating seed or starting clones.
You could also get a switchable ballast that allows MH and HPS bulbs to be used. Or you can get a conversion bulb that allows a MH bulb to be used in a HPS ballast (or is it the other way around?).
You can also go the T5 floro route. They have cool and warm spectrum bulbs that can be swapped out at the appropriate time for your plantz.
The T5's can be just as expensive as a HID though.
I use T5 to start and then switch to HPS once they get a bit hardier and ready to flower. I am thinking about adding some UVb to the mix this time too.
Man you can go broke with this hobby!!!!! Good luck
