I've seen a lot converted sewing cabinets offered for sale - in most cases, the restored treadle cabinet would have sold for more than the converted item is selling for.
The best (worst) item I encountered was a necklace using part of the embroidery control nob from a Pfaff 130 embroidery attachment (it kind of looks like a skull) . They were selling the necklace for $25, the part (unaltered) would have sold for $50.
And the necklace made from welding treadle cabinet keys together - about 30 key total. Individually they sell for $5 - $10. This necklace also had a $25 price tag.
And then the Featherweight table that someone had epoxied the lift out portion in place- again taking something worth about $150 as it was and creating something worth about $10.
Most of the problem with this stuff is location - I have several treadle cabinets I'd give away to someone that didn't want to re-purpose them. But they need to be picked up.