I've seen plants grown with 13w CFLs without reflectors... doesn't mean it's a good way, but it works.
I'd suggest a fully enclosed grow box reflector. Like a round 5 gal bucket, cut the bottoms off for stacking possibilities, line the inside with foil as smooth as you can get it, I suggest gluing it on. Then buffing it smooth and polished. A soft clothe works well.
Then invert that onto another 5 gal grow bucket with your soil%plant. For your top bucket with the light, drill a hole in the middle, put a power cord through it, and attach a socket to the inside. You could probably use a fairly strong spring clip to hold the bulb at a variable height.
If the buckets have a decent lip, vises would hold them together securely, otherwise you could just drill holes near the top, and zip-tie them together on at least 3 sides(a perfect triangle, 60 degree angles, if you can). Otherwise just do it on 4 sides. Or you could use twine, rope, wire, etc. You'll definitely have to do this with the bottoms, as it'll be like stacking 16 oz cups: 'top to top', 'bottom to bottom', repeat.
Also, cover the top of the soil with perlite, or something reflective.