Parts list:
1.  a 4-burner grill
2.  a square-rodded roasting drum with agitation fins inside.  I used a perforated stainless wastebasket, some stainless sheet for the fins (pop-rivited inside) and a steel strap to locate the square rod.  The square rod came from a rotisserie set.
3.  a 30rpm AC motor (excellent speed - no scorching ; got the motor from McMaster Carr) mounted on a a couple of pieces of wood to achieve the right height for lining up with the rod/motor
4.  some cheapie quick-release clamps to lock the motor to the grill when needed.  CLamps eliminate drilling holes in your grill sidetable.
5.  a Lovejoy spider coupler for a quick mate/release between square rod and motor.  Very sweet little piece of hardware, the Lovejoy spider coupler.  It'll give you +/- a few degrees of slack if your alignment is imperfect.  You could probably do the same with a U-joint from a socket set.
6.  a vac or blower system strong enough to cool and de-chaff a couple of pounds of beans.  I use a 5-gallon shopvac, a 30-gallon cardboard drum and a bif, coarse-screened strainer from Target.  Shopvac is nice for quick change between vac and blow; also good for cleaning the inside the grill after it cools off.
I already had everything laying around except the motor ($30 approx) so out of pocket was low.  Old vid:
http://www.youtube.com/watch?v=7uNXxunsGKo
Many, many very neat ideas here, by the way:
http://www.sweetmarias.com/homemade-homeroasters.php