I sent a Nikon D40x to Life Pixel (dot com) and got a "Super Blue" IR conversion for $275. It is fun to play with, both with the IR only filter and without. Focusing is the real trick, I discovered. I remember when old lenses had a red line that indicated the IR focus. (You focused the manual lens normally, then you had to move the focus point manually from the center mark to the red IR mark.) Life Pixel will re-calibrate your body for a standard lens, but if you use any other lens you have to send it with the camera so LP can calibrate it.
Here are some samples... most without a filter, but the one of my patio has the filter. The color ones had lots of channel switching in Photoshop. I highly recommend you watch all of the videos on lifepixel.com. They are very well made and give lots of good information. Beware, if you watch all of the you will probably buy something from them.
No IR filter:
Patio with IR filter
The head and knobs on this fire hydrant are grey, as pictured, but the body is painted bright red. It looks like the IR light passes through the paint.
And a street shot with no filter. No channel swaps here.
ETA: I see now that Life Pixel has a Universal Focusing Calibration for any Nikon with Live View mode.