A $5 HDMI cable will give you the exact same performance as a $100 cable. This is because is digital instead of analog.
A digital signal is not greatly effected by EMI (electromagnetic interference), while analog cables are. This is mainly because analog signals are continuous while digital signals are discrete. For example if a analog 3.54 volt signal is sent across a wire and EMI causes it to go to 3.57 volts, this is be a different noise/color/whatever the data represensts.
However with a digital signal anything above a certain threshold is considered to be a 1, and anything below another threshold is considered to be a 0. A lot of electronics have input voltages from 0-5V. So for the sake of argument, given this range a system would interpret anything above 4.5V as a 1, and anything below .5V as a 0. So if 0V was sent on the line and EMI caused it to become .2V (a huge increase for EMI that would probably not happen in reality) it wouldn't matter b/c its still below .5V. Same thing if it sent 5V on the line and EMI caused it to drop to 4.7V, it would still be a 1.
In addition most digital signals include parity bits to check for errors. So even if you had a crazy high amount of EMI it would detect that there was an error and correct it.
The main reason for expensive cables is that they are super duper shielded to block out EMI. While this can benefit analog signals, HDMI is digital and will not be effected. Over a really long distance certain shielding levels are necessary, but this is typically WAY longer than anything you will use HDMI for. Cat 5 (ethernet) cables are a good example of this. They are able to send data very fast over long distances with very little shielding, however over extremely large distances you need to upgrade to Cat 6 cable, which is a little better shielded. Obviously data is able to be sent over HDMI faster than cat 5/6 b/c HDMI has many more pins/channels and doesn't have to compete with other devices for control of the line.
So in short pretty much all HDMI cables are equal, so buy the cheap ones. This is because they are digital (discrete signal) versus analog (continuous signal). Hope that helps...
is my favorite place for almost all cables.Edited by Xazen - 12/27/10 at 10:30am