These cars are pretty simple to maintain and repair especially compared to contemporary vehicles. It's not rocket science. Most contemporary vehicles don't need the kind of repairs these old vehicles need. One will need to have knowledge/skills/tools or yes it will be expensive unless you want your car repaired by the shop that only repairs Honda's/Toyota's.

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Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT