It depends. If you have lounge access, often there is a computer attached to a printer/fax machine combination and all are free. If you're at a Sheraton with an @linked business center in the lobby, there may be a free fax machine. At Westins, usually the business center charges for stuff and has a self-serve fax machine that takes credit cards. At higher end brands (W, LC, StR) expect to pay, probably a lot.