Placebos are never used in cancer clinical trial, only in prevention trials. Volunteers in a treatment trial will at the very least receive the best standard of care currently available to the public. Medicare began covering participation in 2000 and many states mandate coverage on the part of private insurers. But virtually ever insurer covers the routine clinical costs of participating in a trial. Several clinical trial bills are working their way through congress to enact that coverage into law.
Every clinical trial is different.
Some may pay the volunteers they use. Others may cover expenses such as transportation, food and lodging if necessary. This is a question you should ask the sponsor of the trial. Your doctor is the first place you can look. They may be able to help you locate an appropriate trial and can help enroll you.