Where are you located?
Alex -
Before I bought my first Spider (a 1987 Veloce with "low mileage" - 50k) in 1996, I joined the AROC and got acquainted with some members in my local chapter. Of course this was before this forum became available, and maybe preceeded the Alfa Digest as well. Nonetheless, those local Alfisti were invaluable in pointing toward a vehicle, and referred me to owners of Spiders such as I thought I wanted. The club (and the people on this forum) are an excellent source of information for those who are yet to be initiated to Alfa ownership. The best advice I heard before buying, which proved to be only partly tongue-in-cheek, is that "the purchase price of an Alfa is only the downpayment on the maintenance costs." This can become a truism if you catch the disease and become an Alfaholic, as many of us are. You tend to tinker, learn your car, and make things "better" - all this can cost $$.
Again, I would say, don't restrict yourself to a car with "low" mileage (whatever that is), rather make your restriction have to do with quality of product and model (as you have done - S4 Spider), etc. You will find that restrictive enough, as there are not enough of these cars available for sale that are attractive (especially to a newbie owner) both in price and condition.