A report published by Distimo revealed that "Android have significantly more free apps than either iPhone or iPad, and also the paid apps cost less on Android."
"In free apps, 57% of all Android Market apps are free, compared to 28% of the iPhone App Store and just 23% for the iPad. Only Windows Marketplace has less free apps than the iPad. Palm App Catalog is in second place with 34% free apps. And for paid apps "BlackBerry App World, lands at the top with a rather costly $6.97! Next is Windows Marketplace ($5.96), followed by iPad ($4.65) and iPhone ($4.01). Android apps averaged out at just $3.29 -- and if you want your apps under $3, the Nokia and Palm stores are your best bet!"
More Info: DisTimo