My name is Peter. I am a retired field service appliance technician.
I am afraid I have bad news for you. This is an expensive repair. I am sure it is not your thermostat. I wish it was that simple.
If you have to turn off the main breaker to shut off power to your unit, there are only two components that control where the power goes to your unit.
1.) Electric Built-in Oven Black Membrane Switch
Note how close on the lower left how close the select buttons for both the, "Bake" and "Broil" are.
Part Substitution: 8304266 Cost: $172.00
This component is connecter directly to:
2.) Range Electronic Oven Control Board
Part #: 8303885
The cost is based on Sears parts. You can purchase them over the internet for slightly less.
Only one of these parts is bad. I can not tell you which one without my physically disassembling and testing them.
If I were still working for Sears Home Services or A & E Factory Services and I came to your home. The service call cost would be the part cost X 2, or lets say $220.00 x 2 = $440.00 plus about $200.00 labor, or a bill of $640.00.
The rule of thumb is; " If the cost of repair is 1/3 or more of the original purchase price, buy new".
May I suggest, you go into the internet and search, "Sears Outlet Store". This is a scratch and dent store. You can save hundreds of dollars on a new oven. You also receive a one year warrantee on the appliance.
I wish I could have been more help to you.
Glen Burnie, MD