RCA cable. Been there, done that. Works for audio because it's just impedance and if you aren't running it very far, coat hanger is the shit. near zero impedance, big phat fuckin' conductors.
HDMI, on the other hand, is a 20-conductor protocol:
- 4 pins for USB (data hot, data cold, data power, data shield)
- 9 pins for digital RGB and audio (hot, cold, ground x 3, all digital)
- a couple pins for maintenance (hot plug detect etc) and copy protection (metadata, HDCP, etc)
...all of which sling data around at up to 18Gb/s. I make cable all day long. It ain't no thing. But HDMI is a not-fucking-around protocol. You gotta get everything to work right or it won't work at all.
Flip side, of course, is that if it works at all, it works perfectly which means that if your $4 monoprice cable is getting the job done, a $1600 Audioquest cable will also get the job done.
And nothing more.