DIY is a great option, particularly if you are on a budget and not looking for anything really esoteric. Wire/cable companies generally don't offer their very best cable for bulk purchases, but there are great options that are equivalent to finished cables costing $500 to $1500.
The DH Labs Red Wave cable that @knownothing mentioned is a good example. This cable sells bulk for $40/ft or less (I think Parts Connexion has this on sale for $30/ft right now). Couple with higher-end connectors from WattGate or Furutech, and add some TechFlex (optional) and you have a PC that will cost you $300 to $400 (not including your time) that would cost you twice that as a finished product and is an excellent PC.
If your budget is lower, using DH Labs Power Plus with lower cost WattGate (or Viborg or HifiKing if you want to spend even less) will get you a power cord that is way better than stock cables for about $100.