Some of the biggest markups are on accessories . . . for example, Best Buy routinely charges around $50 - $100 for HDMI cables that ought to retail for a fraction of that, depending on length. The various AV forums have a lot of discussions on crazy markups on cables . . . unless you NEED an HDMI cable IMMEDIATELY, you're a fool not to buy from Amazon or some other on-line retailer.
Try Monoprice.com - HDMI cables running in the SINGLE DIGITS, pricewise. Been using them for a year and a half now for the living room entertainment center, and purchased more for the new downstairs setup this past summer (along with an HDMI switcher which I'm not ENTIRELY thrilled with (connections are a little finicky) - but the cables work just fine!). They also sell other types of cables - USB, RCA A/V, component, stereo speaker, etc. - and pretty much everything is available in a wide variety of lengths. I got several 2' and 4' cables to connect the downstairs Fios box, Blu-Ray player, XBox 360, and PS2 (via converter) to the HDMI switcher, and a 10' from the switcher to the TV (used 2 6' HDMI cables to connect the upstairs TV to the Fios box and the DVD recorder - no HD disc player on that setup).
I mean, you *CAN* pay $70-100 for a box of Monster Cables at Best Buy (one set of component cables; not sure what they charge for HDMI, but I'm sure it's similarly usurious) - but I spent less than half that on half-a-dozen cables, a component-to-HDMI converter, a 5-into-1 HDMI switcher box, and shipping (which took about 48 hours from the time I placed the order to the time it showed up on my doorstep), leaving the remainder for movies, food, entertainment, whatever. Given that I haven't seen a SINGLE unbiased review showing any substantive difference in quality, I'll stick with the $3 cables, and save my money for other fun stuff.