Hi, Thanks for using Just Answer. The most likely cause of your problem is a bad oven temperature sensor. It should read about 1100 ohms at room temperature. The original ge part is no longer available, but you can use a maytag sensor as an alternative. Here is a link to purchase one if you would like. Click here.
If you do go with the replacement you will probably have to cut the wires and use porcelain wire nuts to connect it.
You should be able to replace it without taking the oven out. There is probably a plastic connector on the end of the sensor that will have to come through the hole, so it should be big enough for small wire nuts. If you had a servicer come work on it, I would say around 80 to 100 dollars for labor plus the cost of the part.