You can book a inexpensive hotel in Tsuen Wan area (more likely HK$400 a night) and then take the airport shuttle bus to Airport Expo for HK$12 dollars. Let me know if you need more info.
Sorry, I checked the price of a Tsuen Wan hotel, called Panda Hotel is now increased its room charge for HK$619. A hotel in Tsing Yi called Rambler Garden Hotel costs HK$550. Whereas you can take the A31 bus to airport at HK$18.90