“Transitional car” as a career entrant

Hello people, first of all to my situation: I will finish my studies (BWL) next month. On October 1, I already have an employment contract in my pocket, but in the months in between I will have to keep myself above water with ALG II. For the job (economic audit) I need a vehicle to be able to visit the clients. These are within a radius of 100km, sometimes even more. So there is a lot to be driven. Unfortunately, I don’t have a vehicle, so I don’t have to drive. The problem is that I don’t have any reserves and as security only my signed contract on probationary period. Is there any financing at all possible? My idea is, if I somehow get a financing, to buy a used car and then exchange it after the probationary period for a “Wunschauo”. Because of the many driver’s work, a bit of comfort would be of course nice, from the space available (mainly me and a lot of files must be re In) I would be enough to have a polo-size vehicle in itself. So I’m looking for a cheap, semi-comfortable car that I (if I don’t love it for some reason) would want to sell again after a maximum of a year. In addition, a few tips would be great if and how I can finance this car best. Thank you for your tips!