How to Estimate the Cost of a Service?
I agree with and will paraphrase from Jeremy Parson's answer above/below: Start with an idea of the revenues you can expect from the service, then go figure out a way to create and provide the service at a price that will be self-sustaining (make a profit).
Here's my version of the same answer.
1st - Be reasonably certain of the demand (how much customers will pay) for your service, and the duration of that demand.
Each time a customer pays to use your service, the money you charge has to do three things: pay you back for the variable costs of providing the service one more time; pay a portion of fixed costs(office rent, server time, phone bills, etc) you incur whether you deliver service or not; pay a portion of the start-up costs (R&D, equipment purchases, professional fees, etc.) you incurred to create the service. Your salary (You have to eat, too, remember?) should be included in the start-up and fixed expenses. When the start-up costs are all earned back, then the "break-even" point has been reached. This can take four or five years, sometimes less. Will demand for your service last this long?
2nd - Make a plan to create, maintain, and deliver service so the break-even point can be reached as quickly as possible.
3rd - Decide if there is a high enough probability for profit and if you really want to spend the next few years of your life on this venture. Then act on your decision.