I have opened attached file and I have many ideas how to solve it.
I call such projects peace of cake. It's possible to complete in couple of hours, or maybe even in 1 hr. Maybe even sooner, but I rarely estimate with accuracy less than 1 hour.
Relevant Skills and Experience
Despite my primary area of expertise is C++ and Windows API, I have enough experience with Excel and Visual Basic for Apps for writing macros. Also, I have strong background with mathematics and algorithms
Proposed Milestones
$18 AUD - Macro for calculations
About your suggestion, I can answer follow thing:
nested loops are more reliable, array formulas make more quick code.
What is better, it depends what does matter for you.