Underwater iPhone case for picture?

Taking a trip to Kauai this summer and would like to take photos in the ocean. I'm not looking to spend $100 bucks though. Does anyone have experience with any inexpensive cases or bags for taking underwater photos? I'll only be free diving so 10 meters is deep enough.

Don't use plastic bags. Save the money and buy a lifeproof case they are well worth it if you put the case on properly and follow the directions that come with the case