Thrift stores... I find some of the most beautiful machines for practically nothing at the Goodwill.
When Covid first struck here, all the cheap Brothers at the stores were sold, the thrift stores closed and pretty much any working machine was being sold for around $50-100, when pre-Covid going price for a vintage machine was definitely $20 and under in the area. Just before Covid it was on final closeout at the Goodwill, but a beautiful vintage machine (non-singer) in a stand, perfect condition/lovely decals, even had the instruction book and accessory kit. Originally priced at $40 had not been bought in a month and so was $2 that day -- and I sadly have no room in my house for such things
In this area we have Maxsold, which is sort of like a cross between Craig's List and Ebay. Is meant for online estate sales basically, pictures are posted, bids are taken, all financials are taken care of on-line. Then you go to pick up in person at assigned times, grab your treasures and go. If your buyer fails to pick up their items, the seller still gets to keep the funds and the buyer isn't allowed to participate in any future auctions.
I did indeed recently get a really great vintage machine from the site that needs some work -- but I just want the foot pedal. For $10 it was a great deal. The machine is solid and pretty even if it needs a new belt and case and I've hesitated so far to take the pedal off....
Participation really varies by what part of the country you are in... Here's a current "high end" auction in my area.
https://maxsold.maxsold.com/auction/...27/bidgallery/