Are they stainless or mild steel? If they are stainless, do they use stainless in the welds and on the flange as well? If they are completely stainless, you may be able to get away without the coating. But to be on the safe side I'd get them coated regardless. $70 isn't that much money for coating.

Reason I bring this up is I had a "stainless" JBA header rust to shit on my old Focus. Flanges weren't stainless and the welding material wasn't stainless either. Had the coating been better, I probably wouldn't have had these problems.