A lot of good advice already. My experience is that cable matching to your system is critical. More expensive is not always better. But IMO, cables do make substantial changes and possible improvements allowing you to get the most from your system.
A couple of years ago, I upgraded my CD transport and was considering to upgrade my 30 year old DAC. Before the additional expensive purchase, I decided to invest a bit in a digital interconnect (Cardas Parsec) and a power cord (SUPRA LoRad) for the DAC. For the first time, I actually like my CD playback. I may buy a new DAC someday, but I am in no rush. I have become quite happy with my old DAC. My total cost was $300, not $4K.