Unfortunately, *quality* capture devices are expensive. About $100 per channel for USB, and similar for single-channel internal cards. It gets cheaper per channel when you get a multi-channel internal card, but that's only a good deal if you're actually going to *use* multiple channels.
The $20 USB things are garbage, and deceptively marketed. They'll give you "a picture", but it's probably compressed *in the device itself* and not really HD anymore by the time the PC gets it.
In addition to the list above, I've had good success with one of these:
Acasis PCIe capture card supports multiple HD resolutions (such as 4K60Hz), bringing crystal-clear visual effects to the audience. It also supports quad HDMI or SDI simultaneous input, allowing you to flexibly adjust between different camera angles or input devices. Solve your professional video...
www.acasis.com
PCIE CAPTURE CARD AC-4HDMI (Quad HDMI-1080P60).zip AC-4SDI (Quad SDI-1080P60).zip AC-4HDMI PLUS (Quad HDMI-1080P60).zip AC-4SDI PLUS (Quad SDI-1080P60).zip AC-VS2583 (2 HDMI-4K60).zip AC-VS2584 (1HDMI+1SDI-1080P60).zip AC-VS007 (Dual HDMI-1080P60).zip AC-VS014 (2HDMI+2SDI-1080P60).zip AC-VS049...
www.acasis.com
Specifically, the 4x SDI version, but they also have a 4x HDMI one and a few others.
The thing to watch out for if you're trying to hammer down the price of a multiple-input capture card, is that the cheap ones only have a single converter chip, and a quick-and-dirty switch to choose which one input at a time connects to that one converter. That can work for security cameras, but not for live media production. If you get a multi-input card, make sure that it actually has that many converters, each dedicated to its own input. The ones that I linked, do.
