A 2x2x2ft. square box with flourescent lights works well for me for starting plants and growing mothers. I have 3 lights on top and one on each side and one on the back with the front opening on hinges for access. Raise the plants to within an inch or two of the lights as flouros don't have good light penetration and you won't burn them. Interior painted flat white as Sparrow suggested.
Total price under $200
Likely no insulation required as the lights produce enough heat.You will have to drill some holes to let some heat out. Might need to put in an electric heating pad to keep up the temp during the dark cycle on a different timer than the lights. Do some checking on temps before you grow. Metal halide and propane is overkill, expensive, dangerous and complicated for something this small
Happy growing