Anyone attuned to the Reiki energy by a master can use it, and you needn't become a master to heal effectively. Reiki healing can be done at any time, anywhere, even over great distances. It does not necessarily need to be done only when there is an illness present, it can be done in health as well. The energy conforms to the recipient's needs. Taking a Reiki course can be a wonderfully fulfilling experience.
Cost can run anywhere from free, to literally thousands of dollars.
High price does not always mean high quality, and I advise anyone looking to learn Reiki to please research carefully and find a teacher that suits you. You can start by reading, talking to people locally or searching the Web. I have listed a few links, and at those sites are even more links. Used under License.