Great article on the subject (also covered in The Four steps to the Epiphany by Steve Gary Blank). Concerning the pricing, he explains how to calculate the “bounding box” estimate.

Ask to your early adopters:

1) Assume it was free, how many would you use? (how much does it cost to deploy your product, even if it's free; is there a real neeed; etc...)

2) Assume it costs $1,000,000 how many would you use? (to get this kind of answer: WTF????!!!! The most we pay for this type of product is $50,000...you're done!)