Can't they ask to Alfonso Cuarón if he gently rent them all the paraphernalia used to shoot Gravity?
I've used with good results a cheap Audio-Technica lav connected to a Zoom H1 put in the pocket of the subject. Be aware that some H1s have a strange behavior with a low frequency woop woop woop weird audio noise, well known by Samson itself. I've had my H1 replaced with no cost by them.
I've done the same: brilliant idea, inexpensive, they already done a Kickstarter campaign.