As the others have said, if perhaps indirectly, the big devil is
RUST. Just run from a rusty car. The 1986 Spider is, in our parlance, an 'S3'. These were the most popular generation of Spiders in the U.S. The good news about the S3 is the engine uses Bosch electronic fuel injection, rather than the earlier Italian SPICA mechanical fuel injections. The Bosch can be pretty easily serviced by most mechanics familiar with 1980's foreign cars while the SPICA requires more specialized skills.
In most Spiders, of any generation, the second gear synchros are likely to be worn. This is not a show stopper, but is an annoyance until you learn to shift carefully. Others here can give you a figure for the cost of a transmission rebuild, if they're
really bad. Engines are very stout, and fully rebuildable, but unless the car has a ton of miles it probably will be just fine as it is. However, the engine has been sitting for some years so wake it properly by putting in fresh fluids and turning it over before trying to get it to start. Oh, and in my personal experience, the water pumps don't like sitting for years, and you should probably expect it will need to be replaced fairly soon after you get the car up and running. Brakes may also have stuck calipers after sitting. To summarize, you'll probably drop a Grand or so into the car after belts, hoses, fluids, and getting it running and stopping. The other annoyer will be tracing bad grounds. This isn't a function of bad Italian design or electronics as it is the fact that 1986 was a long time ago.
If you're mechanically handy, Alfas aren't hard to work on, and parts are readily available. Comparatively speaking they aren't expensive.
Here's a good place to find out how to fix most everything:
http://www.alfabb.com/bb/forums/spi...b/forums/spider-105-115-series-1966-1994/85437-spider-technical-faq-digest.html