The Nantucket Diet Murders is the 3rd in the Eugenia Potter series by Virginia Rich. It has dropped to $1.99 at Kindle and Kobo US.
Kindle US:
https://www.amazon.com/Nantucket-Mur...dp/B0030P1WKE/
Kobo US:
https://www.kobo.com/us/en/ebook/the...t-diet-murders