Any capturing card has a line TBC, but I think the OP referred to full frame TBCs which are not present on cheaper capture cards.
And the 300$ blackmagic Blue_misfit's referring to is only the second half of the story (it converts the SDI input into computer files), yes it's not that expensive, but it's also a newcomer. A BD-player costs today some 75-80€, yet only 2 years ago the cheapest one cost 400-500€. Capturing HDMI is also a cheap job today compared to 2009, yet it will be really an expensive hobby if one needs 1080p (as opposed to 1080i capabilities most HDMI cards offer). And paying 300$ for an interface (1:1) is like paying 300$ to add S/P-DIF in to your computer, or DV-in or whatever 1:1 interface; one doesn't pay for the investment in technology, but for the luxury of having a digital "lossless" bridging device/input.
PS: the prices in EU are much higher than those in the States (also the prices for houses
).