The price prediction application that you offer guarantees or not? are you with the skills you have happy to share it for free? but if you have the quality, of course make it commercial, because after all it has a complicated level of knowledge in making the application you mean. Except for promotions that ultimately don't really give any guarantees for use.
I will be releasing it for beta test soon for free of-course. Then after 6 month of running, if i see that it has future, i will add some new features with some minimal fee as i am a fan of open source.