Our Hymer 544 had an oven. It was in the Tec Tower so a bit too high. Our current Hymer has one under the sink. Grills are rarer. A built in cooker is about £630 extra in a Hymer.
Most continental ones do not have ovens because our EU friends find the hobs sufficient. However, UK specced vans do tend to have an oven or microwave. My missus insists on an oven and yet I can go away quite happily for a week on my own and not use it!
Bear in mind the cookers are a constant source of rattles when on the road and, unlike a caravan, you will hear them!
When we changed from caravanning to motorhoming, we sold the caravan to a local caravan dealer and got a bigger discount from the motorhome dealer by paying cash.