I agree with Lawmax. Ususally price difference is bigger for a grade of clarity than a grade of color. However, on today's market white goods become more rare and in higher demand so the situation can change.
I'm still in the looking phase and needed to narrow the choices down but I would try to find a SI1 that was not visible to naked eye. It seems that the difference between a SI1 and VS2 and D and E are not noticible to the naked eye when in a setting (so I guess the choice is more for getting a better value).