I bought the three piece kit years ago from LRS, install was straightforward and fit was very good. I think it was about $60 back then, and if I remember right, it came in a C.D.C. box. Don't know about now though.
If I am not mistaken the "third" part is a lower trim piece that goes under the pony and sits flush with the top of the bumper under the grill. If you have a 99-01 Cobra bumper this is already formed into the bumper itself so personally I only needed the 2pc kit. Hope that helps?