You can get a long way without a product or user base. Look at Kickstarter for examples of ideas that generate money. I'm not saying they are good examples but they are examples.
The real question is what are you looking to create and how much money do you need to get started? Using some of the Lean Startup methodology to gauge the market would be a good idea but don't think you can throw an idea out there and get millions.
If you want to know how much it costs to start a company, the answer is very little. I gave a presentation on how to get from Idea to Beta a while ago, you can view the slides here: http://www.dstrb.com/blog/minnebar-presentation