Best power cords in the $250-$400 range?

In this price range VH Audio Flavor power cords are an excellent value.

Black Sand Silver Max.

I am auditioning this right now and it is pretty much on par with my reference (VH Audio AirSine). Most pc's I have tried can't make that claim!

Look at DCCA cables. Don's theory is that the cord on the amp (ie. the component nearest to the speaker in the chain) is the one to spend the most on. Regardless I have tried many cables, including Elrods, Shunyatas, PSAudio, Electraglide, other DIY designs, and a bunch of the "best for the buck" type and DCCA have by far had the best of all the qualities I appreciate in each of the other brands. Good pricing too, particularly if you talk to Don and ask about demos.
Check out the other threads on Audigon about DCCA.

Stuartbranson,I too own DCCCA pc's, they are very good.
Don is a world class dealer, very flexible.He likes
to take care of his costumer.

Good question...one I'm trying to answer myself right now.
I suggest that you buy a few of these listed power cords used and then test them yourself in your system and see which sounds best to you. You can always sell the ones which
don't float your boat.
A few more which haven't been mentioned yet and which you might also want to add to your short list are; Virtual Dynamics Power One, Audience PowerChord and Eichmann Series 2 eXpress6.