If I take ebay as an example exhaust is £120, delivery £25, which leaves £71 diiference which I can attribute as 'fitting cost'. As I said if you allow that the guy spent a good deal of time with a torch on the flanges to avoid any bolts snapping and then retapped the holes for good measure I consider that a worthwhile expense. Oh and I toyed with getting my local mechanic to fit a bought one it but he still charges £40/hour I might have saved £31 or it might have cost me £9.
I do realise that part of the purpose of this forum is to encourage diy but for me while I could have managed the job I would potentially have had trouble with the siezed bolts and losing a days pay is much more expensive to me than paying a fitter. I also don't doubt there are a number of members unable to carry this work out theirself and hopefully they might benefit from a cheap(er) efficient fitting service.
Sorry if this sounds a bit high horse but I was only trying to help.