For some "budget" means $200 - $300 but I believe one of the best "budget" DACs is the Channel Islands Audio VDA 2. I love this DAC, for $599 you'd be hard pressed to find a better sounding or better built DAC.
http://tonepublications.com/MAGPDF/TA_017.pdf
http://tonepublications.com/MAGPDF/TA_017.pdf