Vodafone iPhone: 499€
AT&T iPhone: 199$ = 127€ (126,285062€ according to google calculator)

With the vodafone model you don't have any extra service you'd have to pay for, just a barebone iPhone, a sim and 5€ of phone traffic. So, at least, to compare both of them you'll have to jailbreak the AT&T iPhone, add 0$ (or 0€ if you prefer, the change is in our favor) to the total price of the AT&T model.

499€ or 127€? I can't really choose which one to buy...

Ok, I'm kidding: to buy an AT&T iPhone you'd have to fly over to the US but, seriously, do you really want to buy an iPhone here at that prices?!?