You won't find anyone who gives two hoots about how long you new exhaust may last, despite what lies they feed you on 'valuing your business' or their own product knowledge. Most people who are likely to be customer facing in this type of industry (car components) are on low wages and just want to get home on an evening, or if they directly benefit from how well the business does (e.g. commission or an owner) are more than likely just trying to get as much cash out of you as they can. Once your back is out the door, you will no longer be their problem. A lot of the backstreet 'performance' exhaust companies just change the name of the business slightly every few years so they don't have to honor warranties, although there will be exceptions to this doom and gloom appraisal I have written.
Do your research.
For Alfas I personally really like the Ragazzon or Supersprint backboxes. Gazella racing do both for between £220 and £275. I recommend either the smallest round or oval pipe tip you can get, or the two smaller twin exit (only one side, not left and right dual-sided) tip. A minority of people on the forum have had problems ordering from Gazella, but there are only in Wakefield so you should be able to get over there easily enough if you live near like me. The advice seems to be buy with a credit card for protection in the event of non-delivery, and also try to insist that the item (if coming from Italy) gets delivered to them in Wakefield, and they then forward it on rather than posted direct to you from Italy.
With regard to protecting your exhaust, and aluminium bracket would be best, followed by carbon steel, followed by brass. Don't get a stainless bracket. Again, you will need to do your homework to find out what is available.
In terms of fitting, I would be doing this myself. The exhaust is 'hung' from a few rubber loops. The standard-type pack from Halfords may have what you need. If not, order the right ones from a stealers and pick them up on a Saturday. Fitting the new exhaust couldn't be easier (he says). Jack the car up at the rear on the side of the exhaust. Leave the wheel on and don't jack the wheel all the way so that it is off the floor - you should still have enough space. Put something very sturdy under the side sill e.g. the spare wheel if it is wide enough and not a space saver. Undo the clamp joining your old backbox to the centre pipe, which should be a couple of rusty bolts or screws and a C-shaped bracket. Once removed, place something under the old backboxes and unhook from the mounts under the car (it may be surprisingly heaving for a tin can!) and rest it on the support. The two pipe sections between the cat-back pipe and the backbox should now 'slide' (i.e. be yanked) apart. Fitting is the reverse. If you have obtained new rubber mounts (that you are confident will fit) it may be easier to cut the old rubbers when disassembling.
Also, bear in mind that if you are connecting a stainless backbox pipe to a carbon steel cat-back pipe, then the carbon steel pipe will also corrode a lot faster, so plan on replacing this.
The stainless system I have is from the cat backwards, so I don't have this problem, and the cat joint is flanged (three bolts, not a slip-on fitting) with a gasket inbetween offering some protection from galvanic corrosion.
For informaion about local 'performance' exhaust outlets read on.
The place I got the stainless exhaust fitted on my Volvo (the one I was talking about in my earlier post) was called Ascar Exhausts, and was just off Westbar police station in Sheffield. This has all been flattened now, but the company moved (under a new name for warrantee reasons) to a little industrial estate next to Centertainment near Meadowhall. If you do go down the local 'performance' exhaust route, I recommend the smallest pipe they do (probably 2.5 or 3.0 inch stainless) and a small, sensible tip. A large bore tip and exhaust is novel for the first 10 miles, then gets a pain in the butt esp. on motorways. Also, make sure they weld enough hanging mounts for the rubbers on the backbox (2 or 3, but you can check this under your car). When I got mine done they only added 1 (to save time and money no doubt) and when I went back, because I hadn't kept up the annual inspection (who the hell does) they wouldn't offer the warrantee. Forked out £20 for another bracket to be welded on. Just be aware.
Cheers fellow AOers