Calculate compounding "interest"

Not really compounding interest, but sort of. Here's what I need in layman's terms. Hopefully someone will understand this logic.

In the attachment, I need to calculate "Est. Purchase" for the number of "value in B1" purchases of each item in Column A for Rows 4 through 30 where "Value in A" <> "". Each time a purchase of Row A (let's stick with A4) is made, the value of the item increases ~15%, so the second item of A4 will be ("value of B4" * 1.15), the third will be (("value of B4" * 1.15) * 1.15), and so on. I need to calculate the total purchase price of "value in B1" items of A4.

So if B1=3, I need C4 to be ("value of B4" + ("value of B4" * 1.15) + (("value of B4" * 1.15) * 1.15)), and then I need that repeated for all rows where "Value in A" <> "". The value in B1 will be changed by the user in order to determine which item in Column A has the highest return value of other calculations that I left out of the attachment (they are irrelevant to this problem), so it will be anywhere from 2 to 20 (or even greater).