Welcome, Nick
You've certainly come to the right place for advice!
Decent 1100s seem to be going for anything from mid £5ks to low £6ks. Have a look at this recent thread from Mick in Somerset, which you might find helpful.
http://www.ukmonster.co.uk/monster/s...d.php?p=556342
Don't let the ethanol issue put you off. This thread will give you more information
http://www.ukmonster.co.uk/monster/s...ad.php?t=54542
Normally, I'd advise using just Esso Super Unleaded but Devon is one of the few places where it contains ethanol. If you're filling up reasonably frequently, (say at least every eight weeks), you shouldn't have a problem as the ethanol should remain in suspension within the petrol. If you leave it any longer - and certainly if you lay the bike up over winter - you should either drain the tank or add a fuel stabilizer specifically formulated for ethanol fuel.
If the tank has swollen marginally, it should be possible to restore its shape by draining it and letting it dry out completely after which it should shrink back. The actual tank is a very irregular shape and the first you would know about it swelling would be if you lifted it, (say to get to the battery), and then had trouble lining up the mounting holes during replacement.
It's not such an obvious issue with the 696/796/1100 series as it is for, say, the S2R/S4R simply because the tank is covered by the separate skins, which effectively hide what's going on beneath, and keep the paintwork safe from damage.
As for the custom tank skins themselves, they aren't manufactured anymore but sets do come up on eBay every so often and buzzbomb told me recently that the outlet store at the factory still have some designs available. (The standard colours are still available as spares from your dealer - at a price!).
Happy hunting!