Travel insurance: 36.85$ USD
Some people get it, some don't. I knew we'd be diving and that accidents happen. I preferred it.
Diving: Open Water (3 days): 295$ USD
We went to a place that offered a discount on accommodation if you went diving at their school. Their maximum class size was 4 and that was ideal because our group was a hand full for our instructor! It was an enjoyable and memorable experience I'll never forget.
Accommodation Total (Koh Tao and Bangkok): 38$
I stayed in a hostel in Bangkok, and we got the diver discount on our accommodation in Koh Tao, with a decent view. The picture above is from our porch in Koh Tao.
This included the metro back and forth through Bangkok multiple times, eating lots of yummy food, getting flat wasted while bar hopping the entire beach of Chalok Baan Kao Bay and I purchased a beach dress off a street vendor. I didn't even use up all of this 190$ budget, I had some left over at the end. Someone being more frugal would do better.
Total: 1402$ USD