3DR Part Sourcing

Hi,

I've built two 3D printers from kits, and now I'd like to build a RichRap 3DR delta printer from scratch. My question is about sourcing of the smooth rods. I have two questions:

1. Do these need to be stainless steel or just steel (such as drill rods)?
2. Where is a good source for 6mm smooth rod?

It looks like the standard 3DR needs a total of 6 smooth rods, each 450mm long.

If I went with 400mm instead of 450mm, McMaster has steel rods at $10.38 each, while stainless steel is $25.53 each. I also found some drill rods on eBay that are 36" long and are $10 each.

Thanks,
-- John