You'll notice that people on this board (and the Alfa digest) seem to spend more 'on average' than people with other kinds of cars.
My experience is with older Alfas (60s-70s) and I think you have to separate two cost categories - restoration and ongoing repair.
A lot of people buy a 20-40 year old Alfa which is in 'running' condition then spend a lot of money fixing all the bits that were ignored or neglected by the previous owner. So, buying a used Alfa and needing to have the gearbox rebuilt (to fix a 2nd gear synchro), having the SPICA reconditioned by Wes I, replacing all the radiator hoses, thermostat and having the radiator recored, replacing trim, recovering seats, etc, etc. Which can all be quite expensive.
Once all this is done - one of two things happen - the Alfa becomes a reliable car which needs probably LESS maintenance than a newer car (the gizmos are much simpler) and hence is cheaper to maintain
, or the owner becomes obsessive and either wants to win a concours or squeeze more hp out of the engine in which case they continue to become money sinks.
If you haven't bought an Alfa yet - it's always cheaper and easier to buy a car from an Alfa enthusiast that has done all the expensive stuff for you. So - look out for a car that has had the tranny rebuilt, clutch replaced, etc, etc. unless fixing the car up is part of the fun for you.
1967 Duetto 1600