I'm a newbie - aren't all Shimano 105 shifters the same?

[LiseB]

I'm trying to get going with road biking and want my first bike to be a used one (in case I later decide that road buking isn't for me, I won't have blown thousands of dollars on a new bike). So I'm looking at a year 2000 Bianchi Giro that's been hanging in a garage for 4 years. Bike shop technician says shifters aren't working properly and that a tune-up may fix them, may not. I need to be prepared to shell out $300 if the bike needs new shifters. They are Shimano 105s. Technician also says they may be hard to find due to bike's age. Do they change from model year to model year? Aren't they all the same?