S234chang is dead on right about component matching.
If your components do not match, no matter what cables you use, you are not going to get good performance from a poorly matched system.
Because I am in the industry, I do not make specific product recommendations in open public forums.
My best advice is try before you buy (AC cords or anything else for that matter). Do as much research as you can. Money does not always translate into sonics. However, this does not mean the best sonics can be obtained with a $50 AC cord. The cheapest reference level AC cord I have found runs around about $600 retail. And frankly, I think that it performs generally as good or better than anything I have tried at any price point.
$600 may sound like a lot for an AC cord, but some companies are trying to get upwards of $2k-3k retail for their cords. Tireguy knows what I am talking about.
There are AC cords under $600 retail that are good. I have not tried them all. There could be one out there that is reference level. I have looked hard, but have yet to find it.
KF