well cfls are "cheap" on power for vegging, but they put only about max of 100lum/W out, so the question should be efficiency
an MH bulb gives you about 120lum/W, a HPS even 150lum/W, so especially in flowering you save a lot if you want efficient light to flower with if you use HPS bulbs instead of cfls since you need 600-800W true Watts of cfl-light to match a single 400HPS bulb, that is the fact
and for the record, i'm not saying you can't flower with cfls, i done it with floros years back on my first try, they flowered fine and my crop was as fine as bad mexican shit
so so much to just flower with a few cheap CFLs