Pfizer offers reimbursements to clinical trial participants, however the study must be conducted by Pfizer and not medical institution where the majority of trials are conducted:
http://www.pfizer.com/research/research_clinical_trials/compensation_trial_participants
Speak up and make sure to be heard.
Remember, without you, the participant, the study could not move forward. You have the ability to address cost reimbursement with the PI (principal investigator). It may not always work, but it’s worth the try. Calculate the cost i.e. transportation, lodging, food, etc. and see what can be covered by the participating institution
More power to you.
Hugs
Marion