It also depends on the country, keyword and industry it is in. You will find the minimum cost varies quite a bit.
It really depends on the keyword you are trying to advertise for. The problem is that even if you can bid $0.05 Google will often force you to pay a lot more in order to get any exposure at all for that keyword. They will simply post a message saying "Bid is too low"...
For extreme uber competitive niche, one click might cost several to tens of dollars. But well, usually, it is only a few cents to half a dollar, maybe.