I haven't sold any yet, but there are a few I purchased with the express purpose of cleaning/repairing and selling. To that end, I keep a sharp eye on E-Bay and Craigs list to check prices on the models I have that I intend to sell. All of them were purchased dirt cheap so I don't foresee a problem at least recovering my monetary investment (I don't and won't care about making money on "labor" as I'm doing this for fun). I'm also not concerned about making my initial investment back - again I'm doing it for fun.
As for where I'll sell them ... I'll probably list them both on E-Bay and Craigs. I think Etsy does vintage machines too and I might check that out.
At the moment though I notice that all around sewing machines on E-bay are not selling for the prices they were selling for a few months ago. It may have something do with folks thinking about outdoor activities now as opposed to indoor activities. I've only been watching prices for about 9 months so I don't know yet if there are any seasonal trends.