[loki_the_glt]

As Othen said, look for a car that's as young as possible; ideally you want a 2.3 Fuel injected model (B230E engine code) without the catalytic converter, and manual box.

Rust is definitely your enemy: mechanical bits can be easily and relatively quickly replaced/repaired but rust removal and replacemnt is time- and money-consuming,plus the car will be undrivable while the rust is being dealt with.

There are a few threads covering this exercise so spending some time reading them will give you some pointers.