We replaced a single oven with a double oven in a river rock wall. We used a construction company for the work - I can't say I was thrilled with everything they did for us, but they did a very nice job cutting the wall and fitting the ovens in. Try RA Briggs & Co. Construction. They charged us a total of $1060 BUT they had to cut around the river rock and refit the pieces together like a puzzle AND build a new inside wall support for the new oven. It took 2 guys 3 days for this work. But If you just increase the size of the opening, have them go up from the existing inside framing and it will be cheaper. Plus they can probably just cut right through the brick rather than piecing brick back together so it will be much easier and faster. Make sure they do not grout the oven in so that you can not remove it in the future for repairs, etc. I would guess your job would be less than half the work ours was. Good Luck!