With any older bike (or even newer ones), if there is no recent history, or its been standing for more than a few months, then you ought to budget for a full belt service (or do it yourself if you can)
Belts breaking/slipping are the worst thing that can happen, otherwise everything else is the usual 'age related' or 'wear & tear you might expect in any bike - fork seals, rear suspension loop arm bolts (common problem in a carbie bike, when it isnt regularly checked)
Electrics can also be a bother on the older bikes, with rear light bulbs often popping, or better still starter soleniod switches playing 'will not work' on that one day you NEED to ride
Not that this needs to put you off, often these can be minor probs just to be aware of in case they crop up.
Personally, I wouldnt pay more than £1k for any carbie 600, and the oldest 10yr plus ones seem to be going for about £800 privately, with about a grand for a good condition Full DSH.
Good luck - and happy shopping
C
