Have a look at Longlife exhausts. There'll be an agent not too far away from you, and they'll make a bespoke exhaust that will then last forever.
I will second Longlife as we had our Barchetta kitted out by one oof their approved agents.
You can get a rough guide price by speaking to the agent/franchise over the phone and giving them the basics of your vehicle and intent.
Once booked in you arrive and discuss in more detail what you would like. Performance, OEM equivallent, number of boxes and choice of tail pipe design.
You agree the price and they just then go to work. Takes around 1 to 2 hours (if I recall correctly).
Our Barchetta has been fitted with a Longlife exhaust for 10 years now with no issues with workmanship, welding quality and fit longevity.
A point to remeber with stainless steel exhaust systems is that by nature whislt good guality stainless steel will not rot there are other issues associated that can cause problems. Stainless is more brittle. Some use thinner stainless materials which can resonate more and are more likely to fracture around joints.
It is a well know fact that an original Fiat exhaust system will outlast most after market quality ones. Fiat originals generally last around 8 to 10 years+ but do cost more than an after market pattern part that may last 5 years or so.
For a normal Fiat vehicle (not a conversion job) I would always suggest getting the best Fiat price (play dealers off against each other), do the same for an after market OEM system and the same for a custom Stainless system.
By doing this you now have a total cost which you can align with how long you intend to keep your vehicle on a "cost per year". The only caviat I would add is that of system guarantee/warranty. Longlife/other stainless suppliers do so for the life of the car/original ownership. Fiat are probably two years but you can expect 8 to 10. Aftermarket is probably 12 months but you can expect 36 or so.
