If you aren't sure if diving is for you but would like to find out before committing to the PADI Open Water course then why not do the 1/2 day Discover Scuba Diving course.
This course is designed for beginners who've never dived before and can be started in the morning or afternoon, although the afternoon is what we recommend as this way you don't have to worry about an early start!
The course costs 1,800 Baht when booked through Koh Tao Backapckers and includes everything you'll need and as a bonus it will count towards your Open Water qualification if you get hooked.