IF you pay for an app, is a one time pay, or monthly?
Application prices from the app store are a one time fee.
Some services might make you sign up with an account that charge a monthly fee, BUT the price in the app store only gets paid once.
If you aren't sure, just close out of the market, open up your browser, and google the fees for said application. Using the Storm most apps just tend to be a one time fee but I have come across a few that were monthly, which I opted not to get.