Sounds like you've just about talked yourself into buying a new machine. As much as you sew, and you've clearly driven this one into ground with pleasure, I'd say go look for a new one. I think $129 is ridiculous for a mere diagnosis. My repair guy charges 20, and will credit it toward the repair. The heart of your machine has stopped beating.
If the motor were still strong, I'd pay up to 100 total to repair a $400 machine. I am with notmorecraft on the cost breakdown for using it. $2 a week plus a boatload of enjoyment. I would go shopping if it were me.