If you want something very sensitive, you might want to look for cameras designed specifically for infra-red and low light. You might not find these on eBay and they probably cost hundreds of dollars. A cheap camera makes a decent proof of concept, though. You can test the camera and viewfinder separately using a TV and VCR/DVD - plug the camera into the TV and you should see the output on the screen. Plug the viewfinder into the VCR's video output (or the TV, if it has an RCA video out) and play something and you should see it on that.
You could add a more powerful infra-red spotlight, but there are limits to the size of lights and batteries you can wear on your head before damaging your neck. The IR LEDs that come with cheap cameras are pretty unsatisfactory, really.