Minimal maintenance expense? The battery alone is a ticking time bomb of maintenance expense, so I wouldn't be touting that as an advantage just yet. I'm not even talking about the peripheral hardware that will be subject to failure, for example the power generation features like brakes.
I bought a hybrid in 2009, and I'll be looking to replace it in a couple of years because that battery warrantee will be going away soon. And I don't even have 20K miles on her yet.
There are only a handful of moving parts in an all electric. The battery is under 8 years unlimited warranty. The battery is covered even if an owner fails to follow charging guidelines laid out in the owners' manual. "Any product that needs a manual to work is broken," Musk said. Tests in labs have shown minimal reduction in capacity over 400,000 miles of driving or a 20 year equivalent of driving. Today the battery pack costs $12,000, so 8 years down the road it will be priced a lot less.
"I've told the Tesla service division that their job is never to make a profit," Musk said. Most auto dealerships make a large portion of their profits from the service department which, Musk pointed out, creates a conflict of interest when it comes to product quality. "I hate the idea of making money because our product broke," said Musk. "That's just wrong."
http://money.cnn.com/2013/04/26/autos/tesla-service-gaurantee/index.html
Base on all of the above, I would bet on minimal maintenance costs for Model-S