Twitter just bought tweetie and made it free. But even before that, tweetie for iPhone cost just $2.99.
Gravity is a twitter client for Symbian s60 devices, but it costs $9.95. Still most users think that it’s unbelievable to build such a great (user experience) app on such a platform (dev difficulties), so it’s worth the money.
So Symbian devices may be cheaper than iPhone, but symbian lacks apps. Developing apps for symbian is more expensive, so apps are more expensive for users.
If It’s possible, I’d like to try out development process on both kinds of platforms and see the differences of dev environments.