What specifically are you testing for?
I suppose in your case since you are doing it in house one could argue you can see if the people are capable but it seems you are focusing a little on style and either this style bunker is appropriate or it is not. Who do you want to make that determination?
At the end of the day, most members will be happy with new sand, but if this style differs dramatically from what they are used to or area comparators (without regard to architectural heritage) you might get some gripes about "style". At some point, our former "restoration specialist" (before we hired Gil Hanse,George Bahto) said he would build test bunkers in different styles to see what we wanted.
Is that the way to go?
At my home course of 27 holes we started on the less played nine in a style completely different than what the members were used to or what was in the ground at other prestigious area courses. To my surprise, most all members were very pleased which gave us a little more license to be bold on the main course. That said, by the time we had started our "test" we were very much committed to what we were doing and who was doing the work, it was just a matter of attempting to educate the membership in the same way the decision makers had become educated. Almost all information was available as to the decision making process were someone interested in the matter.
Our plan called for a payment on a "per-bunker" basis. Short of rock, or any other such circumstance, I have a hard time thinking you should not be able to get a pretty solid handle on the cost of the bunkers.