I actually do consider myself a professional when it comes to sharpening chains, hence my question about what others are charged to have chains "sharpened professionally". 

The 2 main differences in me and a professional shop is 1) I won't tell you when I can have it done, and 2) I don't make any money selling new chains, and consequently I don't have any incentive to grind their chains excessively on my grinder, so I can sell them more new chains. 

And, yes there is a lot of money made in selling chain.  I buy it by the 100' roll and know that even buying that much at a time off of a dealer, who is still making his percentage on rolls sold to me, I'm saving a quite substantial amount over what the general public pays for the same amount of chain pre-made into loops.