First car – need advice Asian/Natural gas?

Hello! Will start my training in August and need urgent advice, because I have as good as no idea of cars. I am now 20, have made my driver’s license at 18 and have previously driven by car from my parents, without accident noticed. Work distance is approx. 30km, otherwise leisure time is rather little. Would natural gas be useful, the petrol prices are rising more and more. Conversion or a car directly with natural gas system? I have a maximum of 600€(in case of emergency!!) available, find the Toyota Yaris from the look very good, I was also told that the Asian cars should be very reliable?! If you look at Autoscout24.de all are but extremely expensive, with car dealers they start at 700€. Otherwise which models would you recommend? How many previous owners Alt/KM stand/How many previous owners? Hope you can help me something more! Mfg Christian