Plastic putty knife
If you're an avid watcher of Debi's videos then you have probably seen the one where she puts paint in the freezer to thicken it up. She uses a number of tools in that video to create a funky layered paint effect, including a plastic putty knife just like these. It is flexible, easy to clean and inexpensive.
They both measure roughly 7.25" long and are either 1.5" or 2" wide.
You can watch Debi's video here on YouTube