When it comes to pricing you have two choices (in my opinion ): price by time or by worth. If it takes you about an hour to complete something like this $5-8 is reasonable considering the quality of the art is rather nice. If it takes you longer, the price should rise. Now, if you think something like this is worth something like $15, then you charge that because that, in a sense, it represents the time, skill, effort, and sensitivities you engaged to create the work.
If you plan to charge points, that is completely up to you how you want to price it. I've noticed that the value of points is more of a mindset than actual worth. Typically if a person is 13 years old and creates art just for fun 50 is a lot. However, if a person is 20+ and creates art for a little extra cash or points to maintain a PM 50 is pocket change. (it's literally something like 60-80 cents).
Anyways, that's my two cents on pricing. People typically have prices too low for art that is worth much more, and hopefully we can all change that in a small way.