One suggestion is a used California Audio Labs (CAL) Sigma. Typically, these can be found on Audiogon for your price range.
Best DAC under US$300
I want to bypass the stock DAC on my mass-market Marantz CD4000, using only the quality Philips trasport. This will hook into an Arcam 6+ integrated amp. I live in India and am looking for ideas on quality DACs under $300 that will work with my humble set up. Gracias, Raghu P.S. I am anticipating grand improvements via this? Do I really need to spend a lot more?