my off button does not turn the oven off...I had to use timers and quite by luck it turned it off..eventually unplugged it. Could you tell me if this is a problem with Kitchen Aid...what part it could be...is it expensive..or what should I do?

Here are the parts
Replacement parts for WHIRLPOOL KERA205PSS2 30`` ELECTRIC CERAN FREE STANDING RANGE CONVECTION OVEN | AppliancePartsPros.com

Cannot say what part is to blame.
Could be the Membrane switch (keypad) (Item 2 in Section 2) re. the key switch is bad.
Or it could be the control board itself (Item 12 in Section 2)

Perhaps try the following first.
Connector Cleaning / Checking
Unplug the unit
Open it up
Remove the ribbon cable from the keypad to the control board at the control board.
Clean the edge connector.
If it is the type where there is not a connector just the insulation is removed, it can be cleaned with a pencil eraser. Do not use an ink eraser as it is too abrasive.
Check the tracks in the ribbon cable for hairline cracks. A magnifying glass helps here.
Would not hurt to clean the connector on the board. Use electronics contact cleaner or isopropyl alcohol and a tooth brush. Be gentle and do not reconnect till all the solvent evaporates.
Reconnect everything and give it a try.