For example, the
DeckLink HD from Blackmagic Design. It's a 133 MHz PCIX card and it captures HD-SDI. It still works with plain old 33 MHz PCI, but it can only do standard definition SDI at that rate. And the best feature is probably its price: $2000. That's unheard of in the realm of professioinal high definition gear. It's low enough that people can buy it and use it for SD work until they can afford to upgrade the rest of their equipment to HD.
One of these cards, plus a dual processor Mac G5 (or a dual-Xeon PC with a PCIX slot, as soon as they get the Windows Quicktime drivers finished), an A/D box, a good SCSI Ultra320 controller and an array of 15,000 RPM drives, and you're all set.
I think you can get all that for under $10,000. Not including software.