You will be working for the duration of the 10-day trip, david4455; make no mistake about that.

You must, accordingly, craft a fee schedule of your services. You may wish to itemize your contributions, or you may wish to quote a daily rate, or you may wish to quote one all-inclusive rate. Once you have a clear idea of your duties and responsibilities you'll be in a better position to present the tour organizers with your proposed fee arrangement.

What is important to remember is that you will be helping the tour organizers make a success of the venture, and you must request compensation appropriate to the level of your contributions and to the general economic level of the tour itself and its participants.

If possible, you could also check with others in your field to learn of their experiences in these matters or with the professional society for your field, if there is one.

Good luck; enjoy the trip!