True enough regarding regional issues and contractors (not just pools - but everything else they do as well).

If you go to the Pebble Tec website, you should be able to find a couple of their "licensed and trained" expert installers. Call around to the ones which are local and a few which are a little less local (you can often save a bit of money by having someone from a more rural area drive a bit further as they tend to have a lower workload compared to those located in major cities and suburbs). See what they charge on their installs for the same finish. Keep in mind, that cheaper isn't always the better option with something that you will be living with for several years to come (and $2000 over the course of 5-10 years isn't too much). At the same time, more expensive isn't always better either.

That said, it looks as though the material is more difficult to mix up than doing something like a two tone paint job (or even a two tone plaster coat). I am assuming application is similar to shotcrete/gunite since you mentioned it is being sprayed. If that is the case, between the first color and the second color the machines will need to be broken down and cleaned in order to remove traces of the previous finish. Then a new batch will need to be mixed and sprayed. Depending on how it goes on, it might add an entire extra day to the procedure, though again - without knowing the application process, I can't speak to certainty regarding that.

It should give you the jist of things though, beyond any variations in the cost of one color to the next there are additional labor costs which are involved to switch between the two colors. Labor costs add up pretty quickly, even before you start to look at including a reasonable margin to keep the lights on.