Inexpensive oven cleaner
If your oven isn't too dirty, here's an inexpensive way to clean it - and you can also avoid the caustic oven cleaners. The night before you plan to clean your oven, place 1/2 to 3/4 cup of household ammonia in a glass bowl, in the center of your cool oven. Tightly close the oven door. Allow the ammonia to remain there overnight.
The ammonia fumes will loosen the grease and grime, so in the morning, you just need to wipe the interior of the oven with paper towels. After the bulk of the grime is gone, wipe again with soapy water, then rinse with clean water