The parts you'll need are:
1) the Sharp IS471 (available for $2 at: http://www.junun.org/MarkIII/Info.jsp?item=46
or $3 from www.digikey.com, and others)
2) a 940nm IR emitter (such as the Fairchild QED-234, available from www.mouser.com for about 50 cents, and other sources)
3) Something to mount the above two items on. You've got a lot of options here. There are several excellent Instructables on making your own PCBs. If you want to try it out before doing the etching thing you can use a pluggable breadboard (not shown) or go with a small piece of perf-board (pads on .100" centers, shown at bottom left).
4) 9 volt batter and battery clip
5) Soldering iron & solder, diagonal cutters (if not going the breadboard route).
If you'd rather not etch, but still want something snazzy you might drop me a line about the very small custom perf-boards I had made at www.pad2pad.com (shown at bottom right), priced at $2 each for the bare boards, postage included).