I purchased a Bluetooth one from Amazon ($10.99) and an Android app (Torque Pro, $5). Great tool for $16 all in. Plus the ODB-II adapter can be used to configure some "quality of life" stuff in newer cars (e.g. the constant cabin backup beep sound on the 2014 Prius).
You will need an Android phone already, but these days that is pretty common (particularly for technical people). Just get the error code and Google it, it becomes pretty obvious what it is.
I know my 2007 Lexus has those programmable options like beep durations and such, but I have only found two solutions - paying the dealership $60 to change them, or buying a $15 android app that changes them. I could do it myself, but the codes (Lexus Personalized Settings) are secret. Did you find a free alternative to modify your Prius settings?
You will need an Android phone already, but these days that is pretty common (particularly for technical people). Just get the error code and Google it, it becomes pretty obvious what it is.