There are certainly some very expensive HDMI cables out there, but I don't know how many of them I would recommend actually spending your money on unless you are dealing with a particularly long run. HDMI is digital, and as such faces a different set of issues than analog. Just because it can carry eight channels of audio does not necessarily mean that its cost should have anything in common with eight analog audio cables of a comparable length, for example. This is because the data being moved is in a very different form. On the contrary, for short runs (when you aren't pushing against the 15-meter distance restriction imposed by the HDMI spec's use of existing DVI technology) and assuming that you are looking at comparable cable quality between HDMI and the multi-cable alternatives, HDMI should be less expensive than the assorted cables it replaces - possibly quite a bit so.
Under certain circumstances, HDMI cable could replace six analog audio cables, three component cables, and a coaxial or optical digital audio cable. In other cases, HDMI might replace just component video and coaxial/optical. I just did a quick comparison of the price of a set of six well-made but not exotically expensive analog audio cables and a similar set of component video cables to the price of an HDMI cable of the same length and from the same source. A 1-meter Outlaw HDMI cable costs $49; a 1.2-meter set of PCA's cost $129, and that doesn't even include component (the shorter length of PSC's appear to be out of stock at the moment, but I think they'd end up costing more than the HDMI cable of you bought three for use with component video) or digital audio. A 6-foot Blue Jeans HDMI cable costs anywhere from $10 to $30; a set of (6) 6-foot analog audio cables costs $90 to $113, a 6-foot component video set costs $45 to $57, and a 6-foot digital audio cable would cost $15 to $25. All of the cables in question are good quality products, and yet the HDMI cable can replace all of its analog and counterparts while still costing less than the analog video cables by themselves. It's only when you start to reach or exceed the 40 foot mark in HDMI cables that prices are going to start to shoot up and performance is going to start to be a concern, and that's purely the result of HDMI's restriction of cable run (something inherited from its DVI video lineage).