Airport is part of the HK MTR system. Airport Express is in fact one line connected to the airport. Yes, it is expensive to take airport express, 60HKD to Tsing Yi, 90HKD to Kowloon and 100HKD to Hong Kong Station. You need to take another bus to your hotel. If you want to pay cheaper, you should take bus to Tung Chung, the nearest MTR station apart from the airport express line. Then you can take Tung Chung Line (need to shift to Tsuen Wan Line) to Tsim Sha Tsui. The costs is 19HKD.