You're making a LOT of big assumptions there, depending GREATLY on where you live:
So are you apparently.
Free electricity to fuel the Tesla
Not unless you live in a city where Tesla is providing free chargers. I don't, and I'm pretty sure my power company won't just give it to me for free if I tell them I'm a Tesla owner.
Well 20 eur a month is close enough to free compared to 220 eur a month that I pay right now.
More like $7 here (1.4 eur / liter).
Cost of maintenance for both cars is similar
Wow, that is a BIG assumption right there. Pretty sure a Tesla dealership is going to charge considerably more for maintenance than a local garage. And very few local garages around here can work on Teslas.
I think by maintenance he meant the (semi-)annual maintenance that all cars go through. Tesla actually publishes the cost on their website. If you pay in advance for four years I think it was 2000 eur total. So 500 eur / year. I can guarantee the breaks, oils, filters and what not that are done on any modern car usually cost above that in maintenance. Repairs are a different topic altogether and should mostly be covered by insurance or warranty.
Also, Elon Musk has stated that the service centers MUST NOT EVER earn profit. They must repair and maintain the Model S at the lowest possible cost while giving the customer the best experience. Tesla gets its profit from sales to end users and other manufacturers, it does not plan to earn profit from service work. This is a major disruption to the usual business model where dealerships earn little in the car sales (hence the low margin business) and earn shitloads in service work. As an example, the local Mitsubishi dealership is 2-3x more expensive than the rally team that I know who rebuilds their Evo X daily. They order the parts from the same central warehouses in EU, doubt that the labor is cheaper, but the repairs are far far cheaper in total when done at the rally shop. So yes, the maintenance is actually going to be cheaper for Model S than for any brand new car that you service at the dealership, not your uncle Joe's garage (here for example that's a requirement for warranty as well as leasing).
The Tesla battery lasts for 10 years + 150,000 miles
You ever had a cellphone battery last for 10 years without degrading?
Sorry, but color me skeptical.
From what I have understood the comparison isn't viable. Industrial grade batteries supposedly have less degradation and the battery LiIon battery lasts best when on average between 30-80% full and has daily usage. Tesla battery warranty for 85kW model (the one I'm planning) is 8 years unlimited miles. The various statements I've heard are that the battery is designed in normal use to have above 70% remaining capacity after 7 years. That is a pretty neat. You'll probably have shitload of car issues in those 7 years with your ICE and drivetrain. I've for example already had to swap the clutch assembly on my Evo X and the estimate is that this is once every 3 years or so. The cost of that is in thousands + labor cost (it's a full day of dismantling and rebuilding). The Model S doesn't even have a clutch.
So if you want to buy an el cheapo ICE, go ahead. If you want to buy a decent luxury performance car, then there is no better car in the world right now than the Model S. From performance and handling stats it's gonna smoke most all the luxury cars and a huge amount of the performance/sports cars. It'll give tough competition to even some supercars. From luxury point of view it has far more space than most cars and it's cheap to own and maintain. Also, as you can use regen breaking most of the time it's one pedal driving and you won't wear through the breaks as fast as with ICE cars, again reducing costs even if not as much as some other elements.