OK. On the one hand:

Purchase new Board: US$25 + shipping
Install New Board: 2 hours work

It all works: All good!

Magnetron is bad: Purchase new Magnetron for US$65 + shipping
Install new Magnetron: 2 hours work.

It wall works: 4 hours + US$90 + shipping.

On the other hand, a brand new 1,000 watt microwave: US$150, complete with warranty.

I admire your wish to reduce landfill, but I have to wonder at the investment in a 10 year old device that is heavily used by your own description.

Peter Wieck
Melrose Park, PA