The trim kit required for a built in adds a lot. For my Viking, which is made by Sharp, the trim kit was more than half again as much as the MW alone... :(

I've always wondered about the the same about built-in appliances. Bare bones freestanding ranges start at under $400, slide ins start at around $1000. Basic wall ovens start at around $800, so you are actually getting less functionality for twice the cost of a basic range. I guess they figure people who have kitchens that accommodate these appliances can afford it?

The Advantium wall oven is not just a microwave with a trim kit. It is built as an oven.

But I can't explain the $1000 difference either.

The Advantium is a speed oven, warming oven, and microwave. You can bake in it - do everything that a traditional oven does except broil. I have one because I didn't have room for both a mw and a second oven. I am very pleased with it. I use it to bake muffins, corn bread, bake potatoes, casseroles, etc. I also use it to keep food warm; it will take quite a large ceramic dish. And my husband uses the microwave function. I think people that don't have one, do not realize that the microwave function is not the technology that the bake/speed oven uses - they are completely different functions. It is ridiculously overpriced but no more ridiculous than a second oven.
Diane