*TESLA* uses that formula for selling their loaner vehicles (MSRP - ($1/mile + 1% per month)). This is *not* the formula that should be used for selling private party.
Take my case for instance, 2013 P85 loaded $102k sticker (at the time, same configuration is about $117k now due to Tesla's price major P85 increases). But taking mine, at 23 months ownership and $1/mile for 62k miles, my car would be worth something like $16k. I believe my loaded P85 is worth much much MUCH MUCH MUCH more than $16k. (and if you want to factor out the $7500 rebate too, then it would be like $9k, LOL).
so regarding that formula, just no way. that formula only works for *basically new* loaner vehicles that are only a few months old with a few thousand miles.
so really its very YMMV what the real selling price is. I've seen P85's resell as high as mid 80s that had decent mileage on them too. Clearly a big discrepancy. Valuating the car is also a major headache for insurance companies too because they also don't have a clue what the real valuation should be. Best bet is maybe to go off of recent Tesla sales on Ebay. Make sure to search SOLD listings (not COMPLETED listings). The range seems to be anywhere between $60k-$80k depending on S60, S85, or P85. Mileage is scattered so honestly I really don't feel like mileage plays a huge factor in the valuation of the car. Its not like a traditional ICE car where the engine wears out over time. Electric motor's (in general) are orders of magnitude more reliable and last much much longer than an ICE engine would. Plus aluminum vs steel, and tons of other reasons why EVs should be valued higher (mostly due to the lack of thousands of necessary parts that could break in ICE engine vehicles). I mean these Tesla Model S's are built to last decades. Battery degradation is also pretty irrelevant with the chemistry they used and their sophisticated battery management system (even at 62k miles, I still get about 258 on a range charge, showing less than 1% degradation and has remained steady like this). So mileage is irrelevant. FWIW there were a few P85s that have sold with high mileage. I know there was one was at 48k miles and sold for around $85k last summer (though P85s have dropped at least $10k since the introduction of the P85D). Honestly I would price it basic on model and options somewhere between $60k-$80k.