With the rate technology is advancing I'd avoid used DAC's unless there is a particular feature set you're after.
New DAC's in your price range: $149 Schiit Modi 2 Uber (USB, coax, optical inputs); $100 Dragonfly Black v. 1.5 (thumb drive size, USB only). Neither does DSD.
As always, if you can push your budget a bit ($50-100) there are lots more options.