Now that you have clearly articulated your @ha Idea and honed the need down you need to analyze the market opportunity. I.e. how many people will buy your product or service and how much with they pay for it in year 1, year 2, year 3, year 4 and year 5.
You will need to brush off your spreadsheet skills for this so get ready. And first and foremost you need to determine a base pricing range.
The only way to determine pricing for a new product or service is to analyze the $ value of the need that it fulfills and then research like mad any comparable offering or one that satisfies a similar kind of need. Examine their pricing and consider hard whether and what value that represents. Value is a simple equation of cost over benefit. The greater the benefit over the cost - the greater the value.
Put in to the equation (and model through your spreadsheet) any price discounts you may need to offer to persuade the early adopter to shift their habits using your offering.
If for some absolute necessity your product needs to be free at first or part of a Fremium offering then make sure you have a clear path to revenues. And beware, prices generally go down much more than they ever go up!
Once you have determined your pricing range - then analyze and size the market opportunity (in that order) by number and type of users, geography - taking into account broad assumptions for churn and competitive split.