Ok so I just found out that it is not "possible" to turn a free android app into a paid app on the android marketplace. You can't simply go change it. Once you go free, you're stuck with free. You can get around it a few ways though.
Firstly, their is always the option of putting ads in your app to generate revenue. Unfortunately, I have not found a solid way of incorporating an add program such as ad mob within app inventor...yet. I can, however, put in my own custom ads but creating revenue from that would be kind of a pain because you need to find your own advertisers. (If anyone wants to buy the ad spot at the bottom of my app, let me know).
Another option is to simply unpublish and republish the app. This is not a good way to accomplish this because it would erase all download counts and all history of comments and ratings. It also would disconnect any existing users from getting any updates to the app. Additionally, it would require going back and changing the official name of the apk file as that would no longer be unique. So this is not really a good option either.
I thnk the route that I will likely take is to create a second version of the app. I will simply rename the current version to "Text 2 Speech (LITE)" and make the new app called "Text 2 Speech (FULL)". Do you think "Full" sounds better or "Pro"? Anyway, the issue that I now have is I need a way to create value in my pro version. If it's the same as the free version then nobody will buy it. Their needs to be some kind of upgrade to it.
Now this upgrade can come in the form of pleasure or pain. What I mean is I can ether add features to the pro app or remove annoyances from the old app. One common way of doing this is to have the paid version remove the ads. What I will likely do is ad some kind of splash page advertisement when loading the program as well as a banner at the bottom advertising the pro version. The pro version will remove both of those. Additionally, I will probably do something like maybe limit the character count in the lite version to only allow enough text for say one sentance worth or so, while the pro version will have unlimited. I would like to figure out how to add different voices/accents to the pro version or different languages, but I have not yet found a good way to do that.
The only problem with this LITE verson and PRO version plan is that by adding in banners and ads and limiting the text field, I am essentially nerfing my current program. This means that any user currently using the free version would actually not benefit from updating to the latest version. They would be better off NOT updating their version. I would feel bad for those who use it and then updated only to find out that the app got "worse" by adding annoyances. Not sure how that will go over with users. Maybe it's not such a good idea? I think I mainly need to focus on figuring out how to add more value to the pro version to justify the cost. Even if it only costs 99 cents or 50 cents, I need to somehow justify that it's worth it instead of using it for free.