I've owned a '78 308GTB for about 6 years now. It's not particularly quick nor that great handling, but the driving experience is well worth the cost of admission.
It's also been one of the most reliable cars I've ever owned. Always starts, never has any serious issue that won't get me home, etc. (The reason the Ferrari took longer than the Minis to warm up is that many owners have disconnected the choke... a malfunction choke... common on the Webers... can damage an engine badly. So we're starting and warming up with open carbs.)
Now, Ferrari guys tend to fall into a couple of distinct categories... purists who go to a dealer for everything and demand all Ferrari parts... and enthusiasts who see them as just another car, don't mind working on them themselves, and are willing to make sensible modifications.
The Ferrari parts you have to buy (swithces and the like) are indeed expensive. But I've placed only two orders to Ferrari in the past 5 years... just for switches and the like. I've spent a lot more with Clark's Corvairs... ;-)
Beware cars that sit... mine was driven regularly (though cosmetically it looked horrible) and that's a good sign that all is well. I drove many low mileage garage queens that needed a ton of work.
I also drove very few injected cars that felt right... and though the QV's are a superior car, the driving experience isn't as good. And servicing them is much more difficult.
Ferrari lore says that non-red cars are much more likely to have been enthusiast owned (and much less likely to have been owned by the gold chain crowd who used them as fashion accessories and deferred maintenance) and I have to say, in shopping for a car I found that to be pretty accurate.
You need timing belts and tensioners every 3 years. That's abouut $300 in parts and $800-1000 in labor if an indpendent does it... or a Saturday afternoon if you do it yourself. I removed the AC compressor from mine (even working perfectly they work poorly) so access is very good. Take it to a dealer and they want to rebuild the carbs, adjust the values, etc... and it turns into a $3500-4000 service. I've not touched the carbs in 4 years (since I rejetted) and the valves have never needed adjustment.
Electrics tend to be weak... an enthusiast provided fuse block upgrade cured 95% of my car's ills. Cost was under $100 and took 30 minutes to install.
The suspensions need to be rebuilt every 60k or so... Ferrari parts would make you sell the car... aftermarket costs little more than going through an MGB front end. I converted to QA1's and coilovers while I was at it, giving me an easily adjusted suspension and getting me away from the non-adjustible, proprietary Konis and spings.
A Ferrari exhaust can be $3000. A custom made one $500. Plenty of room for whatever you like. (I splurged and spent $1000 on a stainless Strebo... just for the looks and the sound)
The #1 reason for poor running is the ignition system. The carb cars have two separate distributors (each with low speed and high spped points) and the engine is basically two four cylinders sharing a common crank. The distributors have to be timed perfectly with each other, advance perfectly in synch, change to high speed points perfectly in synch, etc. A lot to ask for a 30 year old analog system.
A tune up with Ferrari parts will cost $1200 in parts alone. And it's also typically done at the timing belt change.
For that same $1200 I installed an XDi crank fired ignition. It immediately transformed the already good-running car from what felt like a high strung, hot cammed racer into an engine with plenty of low end torque and a power delivery as smooth as a Honda. The purists howl when I open my hood... but I'll never have to touch it again and the car drives better than any 308 I've driven..
In summary, a carbed Ferrari can be maintained fairly reasonably if you are willing to treat it like a car and not a museum piece. The downside if if something does happen it can get painful quickly ( a snapped timing belt could hit you for a $15k engine rebuild)... but then that's not that much different than say a $5000 transmission job on a Mercedes S500... and the latter is a much more likely event to happen.
Bill