On the low season no problem at all. Last May I heard several people mentioning the region of 200-300 baht per night for the best superior rooms. How to go about getting those special deals are a bit more hit and miss. I've heard that it might work to call to any hostel or guesthouse found online and negotiating a price, they might be willing to slice the web-price because it is the low season.
In low seasons you can also play them against each other and possibly carve a little bit off the price too.
In the high season (December-March) you can still find accommodation in dorms easy for 300 baht. As of writing this message I see there is a place called "Phutawan Bamboo Resort" that has double bed rooms for 250 baht even in december.
So I would say yes, there are still deals to be made. And of course you get what you pay for in many cases, and on Phi Phi I would try and find pictures of the place, or if I'm there I would ask to see the room first.