i have a typical jap brand exhaust. mild steel cat back and its still in one piece, no holes, rust whatsoever. And who knows how long the previous owner and owner before that had it for. It costed me something like $400 odd when i bought it + batmbl's 2 in 1 dump/front and your easily looking at under 1k. Why go custom made for - which you have to wait, when you can just buy a 2nd hand jap one and fit it yourself.
I've never had any stainless steel components on my exhaust and personally, i believe it to be too expensive for what it is made to do - flow. On the other hand, custom made can be a hit and miss situation, like black32 said ask joel (cubes).