Compared to the past. With the rise of the Thai baht to the USD, Phuket is getting disgustingly expensive so I've switched back to the Philippines in recent years.

If you just book per dive with a group, 2 dives should be <$50 usd.

Gets more expensive if you want to charter the boat for the day and basically go where/when you want but still reasonable at <$150.

There's a lot more inflation in the prices charged by the resorts over the last 10 years though...