you mentioned the higher prices for advertising leading up to christmas. That is due to ecommerce companies trying to make their year end goals, using major part of their budget in Q4.
However this does not run until the end of Q4 but only until the end of the period when a customer can order something for xmas and gets it delivered.
if you buy on the 23rd, chances are you wont get it for xmas -which is why the companies have cut of dates for the major advertising rushes. I worked for a major global one and their cutoff date was the 17th. After that, spending was cut down tremendously. The will pick up again after xmas but not with the vehemence of leading up to xmas.
So when you look at the higher prices, you need to take that into account. Chances are that your ads directly around xmas and after will be much lower than what you experience the two months before. This relates mostly to the facebook ad universe. On amazon it is the same for categories overall - the vendors are trying to sell and will likely try to do ads across the board, however if you target well, you only run against your fellow writer / publishers. Yet again it is end of year and anybody having goals for q4 will spend budget to reach those goals and in this case likely through to the end.
At the same time you need to think about the mindset of potential customers - when I am on my way home, trying to make xmas with the family, how likely am I going to respond to an ad versus the same ad in january?
I would consider if launching it at xmas is benefitial, and maybe think about a small launch at xmas (to participate in the xmas rush) and a good push for publicity and ads in january when things should be back to normal. hth
