If you HAD to purchase a used (over 4 years old) DAC, what would it be?

>> How is one supposed to make a recommendation when nothing has been shared about what the DAC will be playing with or your listening preferences? <<

. . . or the budget, for that matter.

Yes, many good choices. Knowing your whole system and preferences would be very helpful. It's a bit like saying find me a good desert for $10 without some additional direction. . 

Weiss 501 @ excellent price

Lampizator Atlantic 3 TRP DAC

Chord Electronics Ltd. Dave DAC w/Blue MkII Upsampling CD Player & Stan

PS Audio Directstream DAC MK II

I bought a used MHDT Stockholm v2,  Love it.

I think anything in the last 10 years is a lot better than anything before.  To answer your question, I really wish Bricasti lost their value faster.