a) http://green.autoblog.com/2012/11/30/tesla-adds-replacement-... suggests that the battery replacement costs are much lower ( < 12000 in the worst case for the 85-kWh pack and as low as 8000 for the 40kwh pack). I dont know if this price assumes that you will be turning your old batter in - otherwise I would imagine you would be able to recoup some money for that via selling it to recyclers.
b) Also http://batteryuniversity.com/learn/article/how_to_prolong_li... suggests that the 500 charge cycle number is only valid if every cycle depletes the charge to 0. Assuming that each cycle discharges to 25% - the number of cycles goes upto 2000 - 2500.
Assuming a price of 10000 (Using a medium capacity battery as well as assuming whole sale prices) and a depth of discharge of 25% per cycle and hence assuming battery life of 2250 cyles - you get the battery cost per charge to be 12000 / 2500 = 4.8 . Assuming a 10% tax rate thats about 5.28 dollars per cycle. This number does not seem bad at all.
Tesla offers, for a $12,000 fee at time of purchase, a replacement policy that will replace the battery AFTER 8 years of use, and only after 8 years of use. This brings the price of the 240 mile range model to $91,900, plus tax and licensing. It is not a warranty that replaces the battery if it fails. It offers no coverage before 8 years, and at 8 years one may replace at any time.
Tesla also has cited a price of $40,000 for battery replacement for drivers whose batteries have failed due to not being recharged properly or other reasons. This price is consistent with the lowest wholesale costs of these battery cells on the global market, with no markup for their added value of the battery enclosure, cooling, heating, monitoring, and recharging hardware, thus it is a fair deal and good value as Tesla is clearly not taking any profit at this battery price point.
Tesla does not sell the 85kWh batteries (the ones needed to have a 170-240 mile range) for $12,000. If you hand them $12,000, they will not hand you a battery pack. If Tesla could sell these batteries at this price, they could sell a tremendous number to Nissan, GM, Boeing and others. They could even charge $20,000 and would still have plenty of buyers as it is far below the lowest wholesale cost of the 6800 3100mA 3.7V Panasonic 18650 Li-ion battery cells it contains. Or even better, customers could buy the 6800 new 18650 cells in the pack from Tesla for the $12,000, remove them from the battery pack, and become a wholesale dealer of the cells, able to undercut Panasonic's lowest wholesale price by up to 75%. One could make millions selling new battery cells to laptop battery pack manufacturers that use these cells. It is a sure fire guaranteed profit if, as you say, Tesla is selling battery packs containing 6800 brand new 3100mA 3.7V Panasonic 18650 Li-ion battery cells for only $12,000. It is the bargain of a lifetime. No VC would pass on funding such a venture, it is a guaranteed profit.
The claim that Tesla is selling these battery packs for $12,000 is false. Tesla is not selling these batteries for that price. They will sell these batteries for $40,000 though, as Tesla's Vice President J. Joost de Vries has stated that that is the price for those who need a replacement.
Tesla does offer to deliver a replacement battery in no less than eight years from purchase date for $12000 (February 2021 if you buy today), to the original owner, provided this fee was paid for when the car is purchased, and provided Tesla is still in business. This is not the same as selling batteries for $12000.
b) Also http://batteryuniversity.com/learn/article/how_to_prolong_li... suggests that the 500 charge cycle number is only valid if every cycle depletes the charge to 0. Assuming that each cycle discharges to 25% - the number of cycles goes upto 2000 - 2500.
Assuming a price of 10000 (Using a medium capacity battery as well as assuming whole sale prices) and a depth of discharge of 25% per cycle and hence assuming battery life of 2250 cyles - you get the battery cost per charge to be 12000 / 2500 = 4.8 . Assuming a 10% tax rate thats about 5.28 dollars per cycle. This number does not seem bad at all.