Are you near a Lowe's? Here's an
8' dual tube fixture for $33, and
two pack of tubes for $9.98, so that seems reasonable. The tubes are 4100K, so you'd use 1/4 or 1/8 CTB on your 3200K incandescent lights, but your camera may like that better anyway. I've been told, but cannot verify, that 8' tubes last longer than 4' tubes.
The "industry standard" for professional film/video fluorescent applications is a company called
Kino Flo, check them out for more information on lighting
blue/green screen. Very expensive!
Or call your favorite local TV Weatherperson and ask him/her for a tour of the set. Once there, see how they do it!