For under $150, your gonna have a tough time finding quality bindings. I have a pair of Liquid Force transits that are a medium flex i picked up on Evo for a little under $200. If you're looking for something like snowboard bindings, I've heard good things about Hyperlite's system bindings.
If you're considering Liquid Force, this should help you:
Liquid Force 2014, Bindings, Binding Matrix
Look in Evo's outlet, they always have good deals running there:
Wakeboard Bindings | evo outlet
Also, your riding style has an impact on the flex of your bindings too. My homie (who's regional for Liquid Force) rides a soft binding on cable for tweaking and pressing, while he rides a medium flex binding for boar for support.