I use an HP9500, which looks like it is a color version of the 9050. I would bet good money that the internal workings of the 9050 and the 9500 are identical, minus the color portion. Anyway, the 9500 that I use is a very reliable and high quality printer in my experience. I've done my own cost analysis on the 9500 and found its costing me 9.7 cents per color page at %5 percent black, .7% magenta, 2.6% cyan, and 6.1% yellow coverage. I imagine that you'll probably get around 2 cents per page on a the 9050 because there's no color cost.
Anyway, I think the cost comes from its lower operating cost than most laser printers in its range, but it is old, and the 9500 has been discontinued.
Hope this explains a little bit.