On an experimental car that I was involved in a while back, what we did was use a standard visible near-IR camera like those in camcorders and replaced the fog lights with an IR bulb.

Short wave IR does penetrate fog and rain better so it did improve visibility and in dark situations did work to increase contrast on the display. You're not going to get the heat-based vision that you'll get from mid and long-wave IR though.

Check out some of those cameras from the link I posted and at surplus stores. If you're handy with electronics and know your way around lenses, you might actually be able to rig a mid-wave system for under $1,000.