Col. Mike, on the 9MM magazines I tested the followers are heat treated steel. They did seem pretty durable and very well made.
This is from the Mec-Gar web site about the new 9MM magazines.
Features
Caliber 9 MM
Capacity 10 High Cap
Carbon Steel Tube, heat-treated for strength
Higher tensile music wire spring
Steel follower
Welded butt-plate
Da
, I have only seen the price for them on the Mec-Gar web site and they were right at $30.60 but I am sure that is full retail.