Not really, you get a top of the line 2013 iMac 27" with i7 4gb video card and 16gb RAM on ebay for $1600. That's about half the price of a comparably equipped 2015 iMac 27" ($3,000) - less than half when you factor tax. And both of these models are almost tied when it comes to benchmarks:
https://browser.primatelabs.com/mac-benchmarks
I own both the 2013 top-spec iMac 27 and 2015 iMac 27. This is a good point -- the 2013 model is really good. The only real downside is after you use the retina screen, it's hard to go back to non-retina. This is especially so for text, even more than graphics.
For quite a while you could get a factory refurbished (essentially new) top-spec 2013 iMac 27 from Apple, but I haven't seen those in a while. There are a few 2013 iMac 27s but most have 1TB HDDs, not even Fusion Drive. I would not get one of those. In general I would recommend the newer retina model, but if a potential buyer doesn't mind getting a lightly-used 2013 model, or can find a factory refurbished 2013 with the right features, those may fit the budget better.