Economical car for commuting for 100km easy distance

Hello dear community, I have the following problem: With me soon my dual studies start and I have to commute almost 200km daily between Frankfurt and Mannheim. For me, however, no move is possible, as I also like to drive a car (run often longer distances a day) and the housing situation in Mannheim is very limited. So I am looking for a vehicle at the moment, which is cheap but also reliable. I currently have a BMW E46 318ti Compact. Unfortunately with almost 10l Super on 100km and also with 210000km. In itself my budget for the car would be almost 600-700 euros per month (incl. fuel costs, insurance, tax, maintenance) Thank you already