In what may be a surprise to some, the cost, and popularity, of apps can vary quite a bit across platforms.

According to a new survey from Canalys, the top paid-for Android apps cost more than the top paid-for apps on Apple. Canalys took the top 100 paid-for apps from each platform and totaled up the cost.

In the Android Market, to buy the top 100 paid-for apps would cost $374.37, or on average, $3.74 each. To buy the top 100 paid-for apps made for the iPhone would cost $147.00, or on average, $1.47 each.

Canalys found that the same general conclusion that the top paid-for apps cost more on Android held out when they compared just the top 10 and the top 20 apps. It also held true in each of the five countries surveyed, Germany, India, Singapore, the UK and the US.

The study noted that the apps that are popular on each platform are quite different. Just 19 apps appeared in the top 100 of both.

CP took a look at some of the paid-for apps that both the Android Market and Apple have in common in the top 20. Currently, “Where’s My Water” is number one on both, and costs 99¢ on both. Currently ranked number seven on Android and number two at Apple is Fruit Ninja. On Android it costs $1.26. At Apple its 99¢. Those were the only two the platforms had in common in the top 20.

Paid apps only accounted for about 4% of all smartphone app downloads during 2011, according to IHS Screen Digest.

Apple currently leads Android in the number of apps downloaded each month, according to Xyologic Mobile Analyses, but they predict based on last year’s curves that Android will take the lead in the number of monthly app loads in June, 2012.

Meanwhile, Apple is running a countdown (and contest) on its way to its 25 billionth app download. The countdown clock is at: