Kindle Ebook Marketing

Question:
How much on average do you spend on advertising? Per book?

That is, for successful campaigns, of course.

And is this through adwords?

I know there are alot of 'free ways' of marketing such as free book submission sites.

Any insight would be highly appreciated.

Thanks,
nt1

...this is regarding shorter books - series' maybe - non-fiction as well

Thanks
n1t

I'm sort of a newbie with this, but I tried using an old email list that I had for other project and that worked out well. The cost of it was practically nothing, as I only had to pay for the mailer.