Preface - I’m not answering your request correctly because this one involves a small amount of money. The company is pretty cool, I bet you could get a lower price if you were bundling it with your stage piano.
*EDIT - didn’t see Torsten’s reply from yesterday for some reason - I second his recommendation!
I recently bought a Black Friday half off deal on Kuassa Efektor WF3607 Wah Filter from Plugin Boutique for $14. Not sure if it has a volume related mode, I’ve been using it as a CryBaby with my m-audio expression pedal.
I’ve tried all the alternatives I could find from manually rolling my own by binding the expression pedal to a generic filter to Amplitube’s bundled wah pedal. This one sounds like I expect.
Select from 6 types filter modes:
CB : Dunlop™ Cry Baby*
AX : Vertex™ Axis Wah*
VG : Vox™ Grey Wah*
MuLP : Mu-Tron™ Low Pass*
MuBP : Mu-Tron™ Band Pass*
MuHP : Mu-Tron™ High Pass*