oven cleaning can be a pretty messy job and if doing it professionally you should really have a dip tank and correct chemicals, if you dont know what you are doing then it is easy to damage other surfaces with the chemicals you could be using, we used to do quite a lot for university student accomodation and got about £20 a cooker as we did a lot at a time, most domestic oven cleaners charge about £40 for a single oven with average dirt.