Considering the possible amount of changes and variables, I would lean towards giving a price range, with the lowest fee ($300) covering just a basic layout job with a couple of backgrounds (title and content), plus type hierarchies.
If I were required to create info graphics and/or edit images, create (PPT) animations etc. In the case of info graphics, they should be quoted separately anyway. Finally, whatever price you quote, establish clear guidelines for the number of client revisions covered in your price (usually 2 or 3, max), and as Karl mentioned, the textual content you receive from the client (i.
: basic PPT file) should be complete, and not subject to further revisions.