Financial templates are highly complex and they deal with very large and advanced calculations. These spreadsheets are used in mortgage, loans, and property investments and so on.
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.
Early databases available for the PC market were simple two-dimensional solutions and were essentially designed as a record-keeping system. However, when computing power increased, the advent of the relational database became an affordable option. Applying the rules proposed by Edgar Codd, the Database Management System (DBMS) became a reality, with products such as dBase being widely implemented in the desktop market.
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.