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.
This last point in my opinion is ONE major benefit you must seek to extract, if you choose to engage the services of a developer. S/he should be able to help you develop (in_house) expertise needed to maintain the application AFTER s/he is gone. If you fail to ensure this, all your cost_savings from using the application might end up being spent paying the developer to maintain the application over time in the future!
The claims I make above are NOT exaggerated. They are in fact based on my personal experiences doing the foregoing (a). As an manager in the challenging, fast_paced manufacturing work environment of a corporate multinational (b). As a solutions developer for individuals and businesses who use MS Excel for their work.
The 80ᚼ Pareto principle is based on Pareto's theory that 80% of the results one gets in a particular endeavour will be mainly due to 20% of areas to which one has applied efforts. In business this principle has been found to be true. Your data, properly converted into appropriate performance indicators, will show you where your largest margins come from. You can then channel more time and effort in that direction.