i'd say just get it directly from SLP. When I was looking at H pipes from Mac, i noticed it was cheaper to get it directly from them, so maybe its the same for SLP. Then when i bought my Bassani X, the store i got it from had it shipped directly from Bassani. Go figure
I don't think they sell SLP but 50resto.com has exhaust, I got my h-pipe for $119. You could just get a MAC or BBK x-pipe and then get the SLP catback elsewhere.