You could make money doing something you love (or like [or maybe not so much but just really good at]). It's great to see a spreadsheet come together, and usually a lot better than what you originally envisioned. Especially when the dang thing works.
A popular category of ready-made spreadsheets mentioned earlier, is 'Spreadsheets for Actors'. 'Spreadsheets for Actors' includes sets of programmed spreadsheets that are especially designed for professionals in the entertainment industry, from Actors to Producers. The spreadsheets under 'Spreadsheets for Actors' range from facilitating the managing of budgets to keeping track of income emerging from many sources.
You can also create a calendar with a spreadsheet application and keep it within your budgeting workbook. You can list dates bills are due and you can also use the calendar in accordance with your budget to plan for special items or vacations. Having everything in one place will make it easier to manage your finances and plan for the future.
You'll need to include more than a basic level of development and calculation in your spreadsheet. There are lots of free spreadsheets on the web. Most of which are very simple and easy to build. People aren't going to buy a spreadsheet that they can get for free. Take yours to the next level by adding all the value you can imagine. Then research on how you can offer a little bit more on the development and functionality side.
excel inventory templates
excel budget templates
examples of spreadsheet packages