I'm at 27 months and 49,000 km and I have not paid a cent for service after paying for the service plan when I bought the car. I got the 8 year plan for $4000, so $500/yr. I thought it was $650/yr if you pay as you go, but other people here seem to have paid varying amounts. I've had a drive unit replaced, one door handle replaced, two ranger calls to fix my charging station at home, and a number of other minor repairs, including several I didn't even ask for: a parking brake, 12V battery (twice), 12V jump post, stabilizer link, plus the usual filters, fluids, wiper blades, wheel alignments, etc. that they do annually.
Service has been nothing short of awesome. When I was driving home from Florida last year, I stopped in at the Paramus NJ store & supercharger to charge (no appointment), and while I was there, I mentioned that there seemed to be a new noise when driving at low speed. They sent a mechanic out to take a drive, agreed there was a problem, asked me what was my home service centre (Montreal), and arranged with them to have the drive unit replaced. When the unit was in, they sent a loaner Tesla in a trailer to Ottawa, took my car to Montreal for the repair, and sent it back. It needed to be fixed, but I hadn't even asked them to fix anything - just commented on the noise.
Given the comments here on varying costs if you pay as you go, I'd recommend getting the service plan.