It depends on how handy you are with a soldering iron and how skilled you are at identifying the replacement part.
My guess is that your tech skills are NIL but if it's still under warranty (Don't forget if you bought with a credit card a lot of them double your warranty) get it repaired by Casio for free, or else if you want to cheap out, it's probably a broken potentiometer that needs to be replaced. Any electronic technician worth 50 cents could do this job blindfolded.
Shop around a bit and you'll find someone who can do the job for less than $50 cash money.
Actually check around your neighbourhood for a local Ham Radio Club and see who'll do it for you for cheap. Hell, a lot of them might even be too embarrassed to charge anything for the job. They'll have a compatible part floating around their junk boxes.
Otherwise, if you want to spend 3 times as much for an identical job, take it to any musical instrument shop that offers repairs and you'll get the job done for about $100.
Happy New Year,
Gary