there is no pre-decided answer to this question. it depends on your keywords, target area and your niche
anything is possible in adwords, provided products/services being offered have someone out there to consume it.
I think that it also depends on the type of the business that you want to promote - if noone is advertising you can get really small prices
This is not TRUE at all! It's actually pretty simple to get $0.02 clicks on search and on content it's even easier!