Every March a lottery for US citizens is held for those who enter. Currently 150 names are picked. If your name is picked, you are allowed to race in October of that year. In 1999, a foreign lottery was created. It picks 50 lucky names.
Costs vary from race to race.
Most people go through a few changes of clothes during the race. However, some people will wear their swimsuit from start to finish, and just throw on a top during the bike and run. The most important thing is to wear what you are comfortable in. Most competitors change from swimsuit, to bike shorts to running shorts between each leg. Separate male and female changing tents are provided.