What does a higher crown fee help pay for?

High noble metal - much higher than 50% noble metal content by weight.  At our office, we do not use anything less than 70% noble metal content, unless it's metal free crown.  Some alloys use a lot of gold, imparting a yellow color to the metal.  "Yellow gold" type porcelain crowns give a nice warming affect to the gums.  They are sometimes marketed under the brands Captek or Bio2000.  At higher concentratons of gold, the yellow from the gold can yellow the porcelain--a problem for people who aren't Vita A1, A2 or A3.  (tooth shades are a whole other article)  

No metal at all -  in some cases, you can fabricate a crown with no metal at all.  This is done by using zirconia in place of the metal (marketed by 3m as Lava), or using stronger porcelain materials (marketed as Empress or Procera.  Metal free crowns (aka all-ceramic crowns) tend to cost $100 to $200 more than metal reinforced porcelain crowns (aka porcelain fused to metal crowns, PFMs). 

More shades of porcelain - A well made porcelain crown is a continuous blend of several colors and translucencies.  It should look like a tooth, not like a white chiclet.

More translucency - adding a fine translucent blend is not more expensive in materials, but it takes more time and a more seasoned lab technician.  That's why discerning dentists pay more for their lab fees.

Porcelain front margins - Lab technicians can make the front edge (margin) of the crown in porcelain instead of metal.  That eliminates the gray line in front of the tooth, and the grey darking of the gums over time.  The trade-off is more time, more expense, and relatively poor seal compared to a metal margin.  Usually porcelain margins are placed in the front, so the poorer fit is compensated for by the better hygiene.  (People brush better in the front than the back)  I have not observed a higher rate of failure for porcelain margin crowns.

Ceramic crowns do not have a gray line problem because they contain no metal.

More doctor time -  If there is more revenue per crown, then the doctor does not have to see as many patients, and can afford you more attention.