>>1803295>purchase price: €150 (average lifetime)>maintenance: €450This part of your calculation seems pretty off. Unless you found the worst lemon on the market, you won't be spending 5400€/year on maintenance. Maybe 540, if your car is either rather nice (but then you could obviously do cheaper) or really old (then you depreciation of 1800€/year is nonsense unless you made some terrible choices).
150€/month of depreciation is also only a thing if you want something quite nice and/or recent.
My last car, all things considered, averaged your assumed monthly depreciation and maintenance, but as cost over the full year, over the entire 12 years I had it. And it wasn't even that miserable.
Both your road-tax and insurance also seem way on the high side, but plausible if you're 20 and want something like a 330d. Though that may be more costly in NL. Both combined were 50€/month for my aforementioned old car in Germany.
So totaled I out at 213€/month, roughly. Your milage may vary and current inflation may make it worse, but if you can't beat 350€/month it's because you're doing it wrong.