Sorry, a car alternator is not suitable for most turbine applications. It does not generate enough voltage per rpm to be suitable. Another drawback of DC alternators are the brushes, these cause quite a drag and inhibit easy startup.
A Fisher & Paykell / LG Direct Drive washing machine motor is about 60-75 euros 2nd hand. Some garbage or recycling shops even let you have one for free. The only other thing you need is a 3 phase rectifier which is about 20 euros or so.
I'm currently working on a model using NEMA stepper motors instead, they are about 15-20 euros a piece and have a voltage range that suit 12 Volt applications well. They also generate this voltage at about a 100 rpm, which is what most vertical turbines use.