If you've got the cash, stainless steel braided teflon hose will live with the N20 also, obviously, since it's used for feed lines. I'd guess that you can build a line for $40 or so, with fittings.
I just did an oil line with braided Aeroquip AQP line, but I don't think it's rated for the cold you'd have. Not a bad line to work with, really. They also have a press-fit product line with the AQP material, which is cheaper to use.
What kind of pressures are you looking at in a purge line?