But with an HDMI cable, you aren't sending any oscillating analog waves, nor any power. What you are sending is a low-power digital signal. The digital signal is either on or off, and it is impossible to distort it without ruining it. The great thing about a digital signal is that, even if there is a little noise in the cable (and there always is, no matter how good the cable), the TV will clean it up when it interprets the digital signal. The whole beauty of moving to a digital world is that it eliminates distortion completely.
What this means to you is that there really is no such thing as a "better" HDMI cable. Either an HDMI cable works or it does not. If it doesn't work, you will immediately know it. Your screen will freeze, or it will skip frames, or it will show big square blocks instead of a picture. It will be completely obvious that there is a problem. In that case you need to throw the cable away.
But if an HDMI cable is working correctly, your TV's picture will look exactly the same no matter how much the cable costs. Paying more for a cable will have no effect on picture quality.
Now that you know this, you can see what you need to do as a consumer. When buying an HDMI cable, you can buy on price and get the cheapest one.
That being said, there is one two things you do need to be aware of when purchasing an HDMI cable. First, you have to get the right length. If the cable isn't long enough, it won't reach to the HDTV. Second, HDMI cables have version numbers. For example, version 1.3 of HDMI can carry twice as much data as prior versions. If you buy a high-end HDTV that needs a version 1.3 cable, you need to make sure that the cable you buy supports version 1.3. Otherwise you are not getting everything that the equipment has to offer. In that case buy the cheapest version 1.3 cable available, and it will work fine.