Using Excelville.com, there are no costs associated with selling spreadsheets and you don't need to build and manage a separate site, which works out pretty well. Whatever path you take, I wish you the best of luck. Leave a comment and let me know how things are going for you.
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.
You can build a reputation as an expert spreadsheet developer. This certainly doesn't hurt the resume. Using Excelville.com to sell spreadsheets allows you to set up a profile with your work, biography, and other info that certainly makes for good conversation material during interviews.