not all is audio reactive but if you havnt seen already this is quite agood guide to some existing rpi video-art making projects:
some of these are open source and if not already audio reactive would prob not be too hard to add the features you wnt to them
just to clarify - are you looking for an existing product to buy that does this ? or looking to build or create (diy) something ?
because cost wise a custom solution would be cheaper - basically the cost of the pi and whatever cheap usb soundcard you can get working should do <$40 for sure if you resourceful. (a few of us here could prob give you pointers on where to start too down this path) but custom solutions also take a lot of time !