Yes, with the speedometer installed, and the proper "ratio" configured in the MXL software, the dash with be able to know in which gear it is.
It's not perfect, but it works. I think that you need a neutral switch installed too, since reving the engine while moving will fool the MXL. Not sure about the details.
But asking 210$ for a potentiometer is highway robbery. Now I know why you asked the forum .
It all depends on how much your time is worth.
You'd need to know the size and matting surface on the tranny and then go to an electronic parts store and try them out. They are cheap...