There is no fixed "cost"...it is whatever the finance manager says is "msrp" BMW has no published price (there may be suggested pricing floating around but nothing concrete, AFAIK)...and 762 doesn't sound like a list price (15% off 762 is 648)
Which is interesting...might be the first time a dealer has made up a number, or claimed someone is getting a discount, in order to sell a car... hmmm....
How much did you spend on door dings over the last 3 years? Boston can be a tough environment when parking.... depending on where exactly you live/park
Any chance you'll buy the car at the end? The money is wasted.
Finally, regarding tires.... I almost view this like the 'pre-purchase gas option' when you rent cars- you buy the whole tank in advance, but return the car with 3/8 of a tank and you just paid 60% more for the gas...in 36 months you will likely need tires- but when? If you go 2 years and need tires you are returning the car with 50%. If you manage to get 36 months, perfect.
One other option is to keep the old, worn OE tires and put them back on when you return the car- keeping the partially used tires you have- sell em, use em (and you can go to a non-run flat or other tire at your 'mid lease tire purchase' knowing you can throw those old baldys back on...)
Check out the lease return guidelines:
Wear and Use Guidlines: Exterior
Food for thought, no one answer
A