An invaluable tool in speed, agility and quickness training are the hurdles.  Hurdles can be used to improve your knee lift, stride length, and an assortment of other functions.  After looking at a few of the adjustable hurdles in some of the catalogs, I put together these cheap yet effective ones using 1/2 inch PVC pipe.  Using just a saw or pipe cutter (I prefer the pipe cutter) you can put these together very quickly for about $3 each.  Here is the part manifest that you can use as a guidelines:

bottom:  4 endcaps, 4 8-inch leg supports, 2 T-couplings
top:  1 18" cross piece, 2 90 degree elbow pieces
middle:  2 risers (see sizing variety below)

I made 3 sets of risers for each of my hurdles that can be interchanged as needed.  The first pair are 16 inches bringing the hurdle height to about 18 inches.  The second set 10 inches for 12 inch hurdles.  And the third set are about 3.5 inches for 6 inch hurdles.  This versatility makes it easy to carry the lightweight option pieces to allow for a variety of different training drills.