GPAnalysis is my #1 recommendation to find current, actual comic book sales prices for serious collectors.  While most people are aware of the website they may not know there is also a mobile option for both iOS and other mobile devices.

GPA Mobile is a web-based application optimized for your Apple iPhone or mobile device.

GPA access for iPhone/iOS: http://comics.gpanalysis.com/iphone

GPA access on other mobile devices: http://comics.gpanalysis.com/mob20