Final answer:
The most likely biggest monthly expense for the owner and operator of a high-end spa with a high clientele turnover, including actors and top business people, is salaries.
Step-by-step explanation:
If you are the owner and operator of a high-end spa serving hundreds of clients every week, including actors, actresses, and high-power business people, the most likely biggest monthly expense is salaries. These clients expect a high level of service that can only be provided by skilled professionals. High-end spas typically employ a large number of staff which includes massage therapists, estheticians, and support staff to ensure the business runs smoothly. Salaries tend to be a significant expense because labor is not only specialized but also in direct proportion to the number of clients served. Additionally, based on the provided reference information, the administrative and labor costs for service-oriented businesses like spas or insurance companies are much larger than other operational costs.