Sorry, wrong car...I was thinking GT. A 918 sold at Sotheby's Monterey for $1.84, pre-auction estimate was $1.2-1.6
These cars are made in limited quantities and have an importance to the collector automotive world compared to a 720s which will be worth 75% its orginal msrp in 12-16 month.
on the plus side, a heavily depreciated 720s will be the performance bargain of the century in 18 months.
Probably north of $900k with sales tax. Unless it is Weissach it is not worth 1.6M. At 900k it does not sound like your friend had a Weissach. Have seen people asking around those prices but few transacting though. For me there are nicer cars out now for less money these days. The GT3 RS, GT2 RS, 720S all faster and better looking without the liability of that battery/hybrid. 918 definitely did better than hold its value even if prices today for non-weissach are 1.3M to 1.5M range. The better part of the 918 was access to VIP program. Buy the 911R and flip it. Buy the GT3 RS's and flip them. Buy the GT2 RS and flip it. 10 years of access to limited cars that you can flip. Definitely was worthwhile to those that pulled the trigger. On that alone, I regret not getting one but the cash in the stock market these past 4 years has performed almost the same for me. Just can't drive stocks around fast!