One user at a time : In the instance where there are a number of people required to work on a spreadsheet, they can only access it when no-one else is working on it.
Once you design the type of budgeting spreadsheets you want to use, it will be easy to copy it for subsequent months or years. You can also use just one sheet and create tabs for each month.
A winning spreadsheet could make you a fortune. If you could effectively identify what many people want and are willing to pay for, and can make your spreadsheet easily accessible, you could be cashing checks for the rest of your life.
You may want to create a workbook with multiple sheets for various aspects of your budget. You can have one sheet that keeps track of savings and investments and another sheet that lists your monthly bills.