Hiring a motor for four days costs around 200€ and then that is for a small model that you can maybe squeeze two bikes into (plus the worry of getting anything oily). You are restricted to X km and have the faff of picking it up, dropping it off and then the added worry that it gets pranged.
Between me and my car-less biking buddies we spend about 150-200 a month on train travel getting to and from the trails.
Cost of ownership should be about 110/month before fuel. If friends cover fuel costs I’m not that much poorer, but much more flexible.
And I could sleep in the back of this.