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(DSD) Experience. If you really like it and decide to take an Open Water course afterwards you get a 1,000 baht discount off the PADI Open Water course price.
This course is designed for beginners who've never dived before and starts at 10am in the morning practicing some skills in the swimming pool, then you will head out on the afternoon dive boat that day to explore a dive site or two if you enjoy it and want to take the second dive for an additional 1,000 baht
On the day that you take the DSD you also get to stay at Koh Tao Backpackers Hostel for 250 baht that night.
The course costs 2,000 Baht and includes everything you'll need. As a bonus it will count towards your Open Water qualification if you get hooked and take that course with Davy Jones Locker you will get a 1,000 baht discount off the Open Water course.