If you replace the motherboard, would the new one come with a warranty? If so, I'd be tempted to go that route.
Last year the motherboard went on my Viking 400. I was quoted at least $300 and no guarantee that they could get a new one. Only 30 day warranty on the repair. Since the machine was about 16 years old, I opted for a new machine.
It's tough decision these days. Everything seems to be designed to be thrown away rather than repaired.