Doctor headshots cost between $65 and $750 depending on geography, package and provider. The upper end is likely a complete rip-off unless you’re looking for an extremely specific style. The bottom end is going to produce some truly terrible photos.
When considering pricing, remember to look at a) licensing (who owns the photos) and b) retouching fees.
In terms of licensing, photographers typically only give you ownership for photos that you “buy” from them. This fee is separate from your “session fee,” which just covers the time spent inside their studio. If you want to use your photos on a billboard, or in print, or somewhere else, you may have to pay additional fees.
For retouching, many photographers charge between $50 and $100 per photo. Calculate those fees into your total session cost.
For reference, HeadShots Inc sessions cost between $150 and $400, you get 100% rights to all original photos, and you get one airbrushed photo included (additional are just $25 each.)