And this is not without it's logic, because there isn't just one answer to this question.
The reason I'm writing this article is not to give you that dreamed answer, but to summarize the information I found out there. Yeah, I already did that for myself, spending many hours to look for information. Let me share with you, so you don't have to spend time to find the same results.
1) Let me start with the site, named exactly with the name of the question:
Below are some books, that also may help you better understand how much a good website costs: