It's not just tickling. It's risk of meeting a stranger, and using bondage. It's upkeep of the body; shaving/waxing, mani/pedis, makeup, clothing, bondage eqipment. It's also walking a line of legality, since "sexual services," are illegal here, and definitions and the law can be Tricky. With bondage also comes the risk of being reported for holding someone against their will. It's also that you likely are playing with someone who you might not be interested in on a personal level, and giving them an experience.
So yeah, it costs.