New to American car buying - help would be appreciated

Hi everyone,

I've just signed up here and I'm hoping to get some advice. As my username suggests, I'm from the UK and I've recently moved to Mexico. I've spent the last couple of months driving around in an old Dodge Caliber and I'm finally ready to get something else. When I was living in the UK, I had a few decent cars (Jaguar XJR and MR2 Turbo) and considered myself to be fairly knowledgeable, but here I'm totally lost.

I'm looking to buy a mid/late 2000s car with a decent bit of performance that doesn't cost a fortune to run, particularly suspension wise: Mexican roads are in a terrible state, and I don't want to be spending $2000 on a set of shocks every year as I'd have had to if I brought my Jag with air suspension over. Equally however, I'd like something relatively nice and don't mind paying more running costs than say a Focus or something, I just don't want to be paying out the value of the car every year in repairs.

I've lined up a few viewings for the following cars:

2006 Ford Mustang GT V8

2006 Mercedes CLK 350

2005 Mercedes E320

2006 Audi A6 3.0

All are petrol, all are automatic.

In terms of parts costs and availability, are they all likely to be relatively similar or are some of them considerably worse than others? I don't want to have to struggle to find parts when things go wrong. Is there anything in particular I should look for with these cars in terms of issues? I will of course read the buying guides on their respective forums.

Many thanks