The pro part is very expensive, cost NZD $2.99 just for live tile & icons
I've worked really hard on Weather+, spending hundreds of hours building a great weather app. Instead of making the app paid, I decided to offer the basics for free, and then let users upgrade to a Pro level if they like the app. When you consider the Pro features (over 10 live tile options, 4+ icon sets, and toast notifications for alerts), I think this is a very reasonable price.
If you don't feel like it's worth the cost, don't upgrade; but understand that many people feel the need to support Windows Phone Developers, like myself. You can always signup for Bing Rewards and redeem points for app gift cards, this is a nice alternative to paying actual money.