Shawn,
It's your money. That said, it's you're instructors endorsement. However, I feel that you should be able to choose which DPE you want to take the test with. The fact is that a test is a test, and the same standards apply. If you can pass the ride with one DPE, you should be able to pass with any other.
Personally, when I taught, I didn't care who my students took the ride with. I didn't train for the test- I trained for AFTER the test. It was a given that they would have the skills necessary before they were endorsed... if they happened to have a bad day and botch a ride, so be it. I never got worked up about my pass/fail record. I only cared that they were competent pilots.
If you want to take the ride with the examiner you are familiar with, have a sit down and discuss your feelings with your instructor. Explain exactly why you feel that way, and insist upon choosing the examiner that you feel is most appropriate for you.