Do i need to pay additional for photos if i need to use it for an ebook which is available for resell online
I need 20 animal photos which looks like cost too much if i buy extended license, instead i could go and get it going to a zoo
If the pictures are not the primary value of your work, you are fine with a standard license.
Look here for more information on licensing: https://community.adobe.com/t5/stock/links-for-licensing-terms/td-p/11366788
(Disclaimer: As always with licensing, this is my interpretation of the rules. I think they are correct and advice is based on reading and interpreting the licence terms and on fair use for both the buyer and the artist/stock company, but I cannot rule out that my interpretation is wrong. I'm not an Adobe employee).