The savings _ from using your "in house" expertise _ in terms of money and man_hours alone, will quickly justify the investment you make in "developing the needed skills" _ especially, when you compare what you spend with the cost of purchasing a commercial software application _ or even engaging the services of an Excel VB developer.
"Over_used/Over_spent"(Losses) and "Under_used/Under_spent"(Savings) _ on a monthly basis based on data entered, the program also automatically plotted charts showing trends over a 12 month period.
You can choose to learn how to do it yourself _ or call in someone(an Excel VB Solutions Developer for instance) who knows how. Again, this would be dependent on your purpose, how proficient you are, and/or how much time you have at your disposal. Ultimately, even if someone develops a custom application for you, it should happen with YOUR guidance at every point to ensure that it does EXACTLY what you want it to do, and that you can easily _ with your developer's support/coaching _ learn how to make modifications to it in future, without needing to call back your developer.
For instance if a company had five drink brands in the market but notices that Brand A, which has a profit margin of at least twice the others is in greatest demand, they could (a) focus production efforts on that brand, so that more bottles go out to trade (b) Apply Best Practice/Continuous Improvement initiatives that would result in lower costs of producing each bottle of Brand A so that even though the market price remains fixed, the company is able to earn increasing profit margins per bottle.