You wants a 147. If you're a young lad or lass.. get a 1.6 .. if you're a bit older (for your insurance premium I'm talking about) get a 2.0 ltr.
Whichever one you get check that the cam-belt and tensioner was changed recently. If you're not sure, budget about €500 for it, though a good specialist who can do these with their eyes closed may cost less than that.
The rest is regular car running costs and Alfa's are no worse than any other car. Things will wear out.. so you need to have money to keep it running. If you're skint, you're better off with a little Fiat for the time being..
If the engine is good, then the rest of it is easy to look after. 100,000kms is not a high mileage. My 145 1.8 ltr is on 200,000km and runs perfect.. but that's 15 years old now and it has its own problems with rust and stuff wearing out. A low miles 147 would save you some of that.
Bring someone who knows about cars with you .. so you don't buy one with tyres, exhaust, brakes ans suspension already worn out...
And good luck!