On a previous travel trailer we had the microwave go out on us. (Highpointe) I didn't even try to fix it. My wife and I ended up finding another microwave at Wall Mart that fit the space. It was just a little bit smaller, but it fit. I did have to drill a couple holes from under the cabinet to anchor the feet down. Once in place, I used pieces from the old microwave to fill in the obvious gap. When done, it look really OK.
With a little creativity, you are probably better off just swapping out the microwave for a new one. Depending on what you get, you don't necessarily have to spend $500.
To plant a garden is to believe in tomorrow.
2019 Montana High Country 375FL
2014 Chevy Silverado Duramax, 6.6L Dually