In my area, the vintage receivers on Craigslist go for market value. At this point, I see more 30-something people who are interested in vintage items (not just audio btw), than the supply of vintage receivers coming on the market in estate sales. Yes, I suppose there are some out there in garage sales, but Saturday morning is valuable to me for catching up on sleep. And I think there are people who make a living out of buying undervalued stuff at garage sales, especially vintage items.
Any Marantz or Sansui receivers go for US$300+ on Craigslist here. One reason for the question is seeing which other brands work well with the Mad Dogs.
I did forget to ask responders to mention whether they use the headphone jack or not on each item, thanks !