I suspect the O/P is paying to get most of the work done.
I'm in 2 minds about getting the belts done on a car of this age, TBH it will be a similar price to get a new engine dropped in if the belts fail.
As for a 120k merc - no way - not good value for money - maybe the convo should go like this -
"wot car you got?"
"cum 'ave a look love
"