So, you've worked out what you're going to do - now you need to work out how much it's going to cost.
The way to do this is to do a financial forecast, which might sometimes be called a profit and loss account, or a budget (they're all more or less the same thing).
There's no one way to do it, but the way I'm going to outline here has worked well for me. You start with estimating your sales and cost of sales - on the next blog entry.
I'm going to give the example of a fictitious start-up cafe to help to explain the steps you need to take to develop a strong financial plan.
The section on budgeting on the Business Link website may also be useful to you too.