The large rods are rather expensive, and if you're sure you need those, well then they'll be good. I wanted some big ones awhile back, but cringed at the price and chickened out!
What I've found is, if I use palm, finger, and (opposite hand) thumb pressure, I really don;t need a long rod. THis is opposed to using arm muscles which, for me, usually ends up with the knife scattering or otherwise messing up the tinder pile.
I use the 4" x 1/4" rods from BensBackwoods.com. I think you can get 10 for about $15, bit it's been awhile so don;t hold me to that. Then I glue them into wood, bone, and antler...
Usually if I re-handle a knife or put a handle on a blank blade, I'll make the firesteel holders out of that wood.