Not exactly sure how the title relates to the questions asked in your post, but this pretty much explains everything you need to know about YC: http://ycombinator.com/about.html

Travel expenses for the YC interviews are reimbursed up to $600/team. If you are accepted, you are expected to make your own living arrangements and cover all of your living expenses (rent, bills, food, etc) for the 3-month stint in CA, though this is typically what the YC seed money is for.