New job – car search

Good evening. Here’s no current situation: I’m currently driving a Vw Polo, petrol. From October I’m going to start a new place for work. I’m currently driving about 15 km that day. From Oct. it’s going to be about 100 km that I’m going to travel. If I’d like to have a diesel, with little consumption. I came across the Smart – I was immediately advised not to drive a friend, because I have to drive the highway… That’s why I’m a little unsure and I’m now turning to you… nn give me a few tips?? Ohso, maybe in the end, would have presented me with around 6000 €, what the new vehicle should cost… Lg Athichen