I have two ICE vehicles and I change the oil for each myself according to the manufacturers' recommended maintenance schedules. Changing the oil for one car, once, costs $42 for oil and $16 for the filter. The yearly cost for one car with a 7500 mile recommendation is about $116 (two total changes a year typically, though it looks like I did it three times last year for that vehicle).

I've had a Model 3 for 2 years now. Total cost of ownership (excluding insurance and registration fees): $1578. That's ALL costs, including electricity used to charge the battery. The majority of those costs: a set of new tires at $1050.

As far as a lack of after market parts go: what parts would you expect to see on the after market? The things one needs to buy for a Tesla are represented quite well in the after market. Tires, brake pads, cabin air filters - plenty to choose from, and widely available at any auto parts store. Tell me more about this "significant gap" of after market parts.