Generally speaking I don't accept a child into care that is on a completely different diet than what we normally serve because it becomes difficult as the child grows and wants what the others are having and I have to be the mean one and say no. I also find those with a diet regimen different than mine tend to have other attitudes that are different or tend to be more fanatical in a sense about some things that maybe I place less importance on - in general we are not on the same page as far as what is wanted for the child so it is rarely a good match.
At the same time I have done specific foods due to allergy/sensitivity and as much as possible mom provided the alternative to what we had such as milk or a specific brand of a food that didn't contain the offending ingredient so child's meal didn't look as different and everyone soon understood that if said child ate the forbidden food it would make their tummy hurt real bad.
I never gave a price reduction and never had anyone ask for one. Most were grateful that I would accommodate the child. But I only took those that were easy to integrate not those that required a separate lifestyle.