Single post in Reverse "Enter Custom Amount"

I wasn't really sure what to title this suggestion, my apologies. I would like to propose a section on the ZC purchasing page that acts as a reverse of the enter custom amount. Whether you can actually purchase via it I'm unsure (I don't know if that coding is possible), but just a calculator would be great, honestly. Let's say I have a $25 USD budget for ZC. I enter $25 into the box and it tells me the exact amount of ZC I can purchase at the moment, with the best deal. Even if it's a weird number like 1236, I think this would be super helpful. It may just be a stupid personal want, but I would be really happy to be able to say "okay, I'm going to spend X EVERY week on PFQ," instead of buying packs - because the price fluctuates. This way you can spend what you're willing to and just get however much ZC that is.