needing a simple mp3 audiobook player that works with dropbox

Hi,
I have a student who wishes to read an mp3 audiobook that is contained in a zip file within his dropbox. He is a beginner iPhone user, so I'd like something simple that can play a multi-part mp3 audiobook from dropbox and have a bookmark option and possibly a variable playback speed, although I don't really know whether he'd use that or not. I am aware of voice dream reader and I have recommended that, but it's kind of pricy just for someone who wants to read audiobooks. Is there still a light version of voice dream reader I could set him up with so he can make sure he likes it first? If not, can somebody recommend a comparable app that will let him listen to audiobooks in his dropbox?
Thanks,
Moop