Add a cost estimate (hourly?) to the create cluster page

[esmet]

Maybe this should go in the confirmation prompt, depends on #11

[tmcallaghan]

Would be nice if it was updated as I modified the instance type and quantities.

[esmet]

It seems amazon doesn't provide a nice API to get instance pricing. May need to just hard code the costs. Not sure.

[tmcallaghan]

I don't think you'll find anything via an API, hard coding is fine.