I'm having difficulty finding just broad "rates" for original 2D art for something like a 2D platformer. Or what is average I should say.

For instance I know that if I look long enough I could find sprites for some$10 to $20 a pane. But then that artist would have a decent chance of not being interested in drawing environment or tile art, meaning the next guy will end up costing more as he needs to match someone else's style(or need to ask for resubmits).

Another thing is I see people charging by the hour, and have no idea how much someone is expected to be able to get done in an hour.
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So I would pretty much like to see articles along the lines of costs for commisioning/contracting/outsourcing art for a 2D platformer or something of similar scale in article form or even a spread sheet if possible. It's safe to say that I know very little about the topic, and my google searches aren't very useful with what I do know.

Contractor artist rates vary quite wildly. In my experience, generally in house contractors are paid hourly while outsourced art is commissioned. Experience level and location of the artist are the two big factors. I know that in Texas a talented, experienced artist can easily request at least $30/hr. An inexperienced artist is going to be less than that, someone in say California or the east coast will probably run higher, and someone say in China is going to cost a fraction of that.