Khao Lak is bout 100km north of Phuket, and about 130km from Krabi. It;s fairly easy to get to by car or taxi, and if you go in the low season ther's some great bargains to be had.
I stayed at the 4 star Moracea Khao Lak Resort and paid 1600 Baht for a deluxe room including a fantastic buffet breakfast.
But the monsoon and rainy season is called that for a reason; so you must expect some rain even though the skies usually clear quickly and you'll get some sunshine. Is that a compromise you can accept in return for a discounted price? After all there are various restaurants, swimming pools, an exercise room and a spa to keep you occupied. There's also plenty of places to visit nearby. This is how I spent 24 hours in Khao Lak.