By my calculation, my car (including running costs) comes down to about 300 eur/month assuming I keep it for 5 years and get at least 1000 eur back when I sell or scrap it. (Reality: I'll probably get more out of it, or keep it longer)

Rentals start at around 28eur/day, so if I rented one every weekend (saturday+sunday), that'd be 224 eur plus fuel. Hardly cheaper.

Of course I don't travel every weekend, but when I do, it's more likely to be friday+saturday+sunday, and I do make week-long trips (and longer) a few times a year so it balances out, more or less.

Owning a car means I don't worry about making reservations, fetching and returning the vehicle, etc. It's always near the door, and I can go on a whim if a sudden need comes up, like it did just today.