I am a man who can appreciate the honesty and sincerety of standing up and shouting, "Hey, I'm cheap and I don't care who knows!"
My name is Chris, and I'm also a compulsive cheap traveler.
Here is my best advice.
www.westcoastdivers.com . They are located in Phuket (as are about 100 other dive shops) but I went on their liveaboard and had almost the best time. I couldn't stand one of the instructors in the crew. He was a rude, know-it-all who needed to be slapped down. I came this >< close!
Any hoo, the diving was fantastic. Only three whalesharks in four days, and five manta. Tons of other stuff but too much to write about. Check out their website. If I remember correctly, with the exchange rate, I paid roughly $450 US for the four day/four night, 14 dive cruise. Included everything to survive. Bring your own towel and personal items. The food, tanks, etc.
If you want more advice on where to stay, just ask. I usually stay in guest houses for around $10 US. I've actually stayed at less expensive and during the Christmas season!
Now here is a secret, are you a DM or OWSI? If you are, you can go standby on some of these boats and if you can get on, you would pay the bare minimum but you would be asked to help out with some of the divers or on the boat. But, don't worry, everyone helps each other out.
I would like to know how things turn out!
Chris