When I licensed my cover photo (a very famous photo of Louis Armstrong, once used on the cover of Life), it was $400 for a print run of a thousand. When I informed the very helpful agent at the rights agency I was POD and didn't know how many I would "print," he said if I went over a thousand to call and we'd work out another pay. (I told him I'd like nothing better than to have to call him, since that would indicate nice sales.)
A photo from Trek for as many books as this might be moving, might be pretty costly. Some books are gonna sell because of the cover, to browsers. Others are going to sell to fans who HAVE to have it regardless of cover. the author might have gambled well on this issue (cover cost). I'd still want a better one because it was my product with my name on it. I wish I could figure out how to post my cover here. I am pretty proud of it.