This doesn't need to be anything complicated. You can use a spreadsheet like Excel or use the free Open Office suite, which will let you get started without spending money. The most useful budget for a business is easy to use. Try setting up your budgeting system by using a template that has been designed for the spreadsheet program that you chose. A Cash Flow template is a great way to see an overview of the profit the business is making.
Spreadsheets are very flexible, and you can use the information in your initial cash flow budget to build other worksheets that will help you analyze your business finances. For example, in Excel you can create additional worksheets like 'a Break Even Analysis' and 'Quarterly Self-Employment Tax estimates'. These and others are useful to help your comprehension of your projected budget totals and your actual experience. Its worthwhile to link these worksheets to your basic budget. This is because, when the actual data becomes available, as opposed to just estimates, you can adjust your business budget accordingly.