According to my husband, he spent around $100 for the Viking Emerald 118 he gave me for Christmas four years ago. It has not caused me any trouble at all, runs like a champ, and handles bulkier seams with relative ease. It sounds like you have a ton of good suggestions here (I like the idea of introducing them to older machines or checking with a local guild) so I am sure you will figure it out. Good luck and what a great idea to auction off your knowledge. Way to pass the torch!
