No i don't include extensions with the gel polish, if your client wants a gel polish over extensions charge what you would for the extensions with a polish plus what you think is acceptable to bring it up to a price worth doing it for.
Gel polish manicures should be a completely different service from Acrylic or Gel extensions. Think of it from a money making perspective, you would be losing a lot of money by offering them both combined.
If your clients come back for an extension infill, that is your opportunity to ask them if they were happy with how well the polish lasted on their extensions, then you can recommend a gel polish and make more money by performing them both separate!!
Hope this helped! xx