I'm not so sure about this.
For modern printing methods, the cost of printing either is barely distinguishable. Neither is expensive. If you use either in a book, the increment of going to using them on every page isn't big. The old days of plates being bound together have gone. Colour plates maybe, but not B&W.
Secondly, the cost of producing drawings can be a lot more than photographs. I can do photographs myself - decent lighting and anyone can. Drawings however will need a graphic artist involved. It's not a huge cost, but in this particular case it's in favour of the photograph. Of course, I also need to produce the piece before I can photograph it.