exhaust systems summary please

[Kevin Hollis]

I'm starting to sound like a farty old man so will probably patch the 
exhaust up initially but will need to replace soonish.

Would someone please post a summary of the various exhaust options that 
I have. I'm guessing not that many.

Any recommendations ? I'm not interested in increased power or noise, 
plenty of that already. Also not interested in looks, only value for 
money. :-) I commute 90 miles daily and  the bike is left out in all 
weathers as I have no garage.

Thanks
Kevin