You would need a pro account before you can introduce in app purchases like that, otherwise you can set up two versions of the game, a lite version and a full version.
I have no idea what you can do in Corona (license wise). Your best option if you don't want to go Pro is to create two versions of your game in GameSalad. A free lite version that has a few levels, and a paid version which has all of the levels.
However you may experience trouble selling an app with GameSalad adverts in it, adverts you can't get rid of until you go Pro. I know people here have and are selling apps with the ads in.
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@Justin007h Hi, you can allow users to unlock levels using In-App Purchase behaviours but you need to be Pro to use this.
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However you may experience trouble selling an app with GameSalad adverts in it, adverts you can't get rid of until you go Pro. I know people here have and are selling apps with the ads in.