My daughter was a recruited athlete, and was at the 75% or higher as far as GPA/Test scores. She received a range of merit scholarships from every D3 school she applied to. I don’t think there is any way to know how much, if any, is due to her athletics. However, I would say that admissions probably looks not just at the numbers, but also at a student’s potential contribution to campus life. Most of the coaches made it clear that they do help with admissions. So, if a student is a borderline candidate but is a desirable athletic recruit, s/he could gain admission with the help of the coach.
I think it’s perfectly reasonable to communicate with the coach that you are going to apply regular decision because you need to consider finances.