Spotty, in most (if not all) trials, the device is donated and there is no cost to the patient. In some, where the patient is obviously qualified based upon the selection criteria, the surgical and professional costs are also covered.
It really depends on the trial though; I had the Charite implant within the FDA trial in June 2004 and had to figure out how to cover ALL the charges except the device. I fought "Blue Corpse Blue Sled" and won.
Here's a link to most of the ongoing trials, you have to call each one for now to check on costs. See
here.