So having recently spent $99 on a Kindle Daily Deal ad on Kindle Nation Daily, I thought I'd report back my results from it.
I must say that my book only had five reviews on Amazon.com when I placed the ad, and three of them were two stars, so I'm sure if it was reviewed better then it would have sold more.
The picture below is from Amazon.com - The spike in sales is due to the ad. I was averaging 3 sales a week on the .com site, and because of the ad, that went up to 34. The profit on $0.99 is about $0.35 per book.