Quarterly Multiplication

I have a 10 year table broken out by month and I'm trying to perform a calculation that should only occur at the beginning of each quarter. In addition, the amount to multiply should be 100$ in the 1st quarter, 75% in the second, 50% in the third and 25% in the fourth.

I have attached an example worksheet showing just the first two years of the results I get (without the prorate) and also shows what the expected result should be. I prefer not to use a bunch of nested IF statements since I may need to get to a more granular level at some point where I'd need to do this on a monthly calculation.

Thank you both for these solutions, both worked.

Bebo, this was exactly what I needed and although the NFLSales solution also worked, I did not intend that the price table be used, that was meant to calculate the values I expected, but I failed to make that point clear, but with the extra table the solution was also workable.