Last winter I built a box using spiral bulbs. Major cost was for the bulbs and a small blower; the box itself was made from a 1/2" MDF "handypanel" from the home center, plus a piece of plywood left over from a previous project. Total cost less than $100. It works quite well - 4-10 minute exposures for VDB or Pt/Pd. Impact on utility bill is negligible (but then I don't leave it on to grow plants continuously). My box uses 6x27 watt bulbs on 6" centers (2 rows of 3), with the spacing between the ends of the bulbs and the top of the printing frame about 6".
A few weeks ago at a workshop I used a box based on 6x36" "actinic" tubes. Printing time was 4 - 15 minutes for Pt/Pd. There were two boxes that the instructor had built by a friend - don't know what they cost him, but the woodworking was furniture-quality - much better than my painted MDF. Both boxes had problems getting all the tubes started - solution was to look, and then reach in and tap the tubes that wouldn't start. That's a problem with tradtional fluorescent tubes that you don't have with spirals.
I thought about using the pre-made fixtures at Home Despot, but frankly they looked pretty cheesy, and in the end the box that I build offers a larger exposure footprint at lower cost than I would have achieved using those units.