There is a one time fee for each app. Be careful about excessive data usage, there is still some debate on whether VZW will charge if you use massive amounts of data each month. Torrents probably aren't a good idea.
looked at both of the apps and they both seem to be about equal. there's actually free versions of the two. the only difference between the free and the pay for apps is that the pay for apps allow you to access "https" address where as the free ones do not.
there was also one negative review about PDANet... it says that it's "free for a limited time." any truth to this?