From my own experience - when I bought mine, it had a "clutch assembly" installed at a Ferrari dealer a few months earlier. Clutch assembly meaning the whole bellhousing with clutch plates and pressure plate in it. It goes for about $3300.
So I thought the clutch was good for a while. Lo and behold, the clutch failed on me 3 times within a couple of months - fortunately the clutch is very easy to work on for DIY because it's at the end of everything as opposed to in between the engine and the transmission like on most cars. Basically the "triple seal" failed once leaking transmission oil into the clutch. Then the slave cylinder seal failed, dumping brake fluid outside the car (and you gradually lose the clutch in about 30 seconds). And finally the thrust bearing seized, taking out the "fingers" on the pressure plate. All these parts are outside of the clutch assembly, and so were about 20 years old. All this happened in about 6 months, but I have not had to touch it again since then - it's been 3 years.
Ferrari parts are truly expensive - around 3-10 times more. But if you can turn a wrench, it won't be too bad. Aside from the new clutch assembly which was already on the car, I spent $1000 on the thrust bearing + flange (from Hill Engineering). Typically thrust bearings are <$100 items on regular cars. Same with clutch packs - $350 would buy you an entire clutch pack normally. Just saying.
So I did not spend any $ on labour during the 3 times when the clutch failed. And I wasn't stranded at all - I ended up starting the car in first gear and drove home slowly late at night.
There are really 3 things important on a car like this - engine, transmission and clutch. The engine - you should be able to tell how well it runs while testing driving it. Same with the transmission - but do expect 2nd gear to feel notchy - that's just how all manual Ferrari's are. But gear boxes on this car are known to be very expensive if you ever need one.
Someone might have already said FerrariChat.com and FerrariLife.com are the best sources of info. There is a huge base of drivers passionate about the 348, and most of them work on the car themselves (with lots of tips on these forums). RicambiAmerica.com is where most Ferrari owners in N America go to for parts.
So all in all, some work is to be expected for an older car like this. There is of course the 30K miles / 3 years recommended timing belt change (about $4K or some people DIY). But once you start driving it with the Italian opera singing 6 inches behind your head, you will wonder why you have wasted so long =-)
Good luck.
