Check your local craft fairs- one I just went to had stuffed animal cleaning/restoration for $30-$40. Otherwise, it might cost closer to $85-$100. Another option would be to use a tutorial (ex. Restoration Instructable) and try to do it yourself!

This is a screenshot from the manual- hopefully one of these will fix it.

Here are a few things to try: (1) Turn it off, unplug it from the wall for at least a minute, and plug it in. (2) You may be hearing the Intelligent Acoustic Control. To turn this function off, hold down "Metronome / Rhythm" and "Pianist Style", press the G#3 key to turn off (G3 to turn back on) (3) You could also be hearing / missing the "Sound Boost" function. To turn this function on, hold down "Metronome / Rhythm" and "Pianist Style" and press the C4 key to turn on (C#4 to turn back off). (4) Finally, you could try choosing a different "Voice". Try switching between Grand Piano, Bright Grand, Mellow Grand, and Stage Piano.

If you can remove the painting from the mat, do so, and use water to dab at the entire cloth mat. Then, dry the mat while pressing it under books or something else flat and heavy. If you cannot remove the painting, do not paint over it. You could maybe try putting new fabric on top of the old cloth mat instead.