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.
Spreadsheet: A table of rows and columns, free for the entry of data, or formulae for calculating actions on those data. Each row or column is said to contain many 'cells' and these cells serve as 'homes' for every shred of information.
You'll need to develop good marketing material. Things like demo videos, which you can find plenty examples on YouTube, screenshots, and keyword rich descriptive text help people find your spreadsheet and communicate the value that sets yours a level above the rest. Excelville.com actually allows you to upload your spreadsheet with all of this marketing material in an easily searchable and user friendly website.
"Spreadsheets for Small Business" is a complete package of ready-made spreadsheets that optimizes and facilitates a series of business processes such as sales exec commission tracking, calculating business expenses and planning budgets. The "Spreadsheet for Small Business" package incorporates valuable programmed spreadsheets such as "Small Business Expense Spreadsheet" - provides accountants and tax-preparers with a complete report on relevant business expenses; "Producer's Budget" - helps users to establish budgets and keep track of their spending; "Monthly Personal Budget" - designed to track daily, weekly and monthly spending for individuals.
examples of spreadsheet packages
blank spreadsheet templates
spreadsheet templates for tracking