I have talked about the following in the past, but I think it is worth repeating it with adjustments for an even more inflated price:

AMZN is trading as if it was generating 7% profit margins.  If we apply this to next years $120B in projected revenue, it would generate about $8.4B in profits for  $18.10 EPS, giving it a still high multiple of 24.58 at todays PPS, but I far more reasonable than its current PE north of 180. 

A profit margin of 7% is higher than Macy's (5.4%), WMT (3.37%), TGT (-2.2%).  It is a bit lower than GPS (7.68%), HD (7.63%).  Since AMZN is a retailer that carries a wide variety of products in many retail segments, I would venture a guess that AMZN will eventually end up with profit margins that resembles the average of all of them plus a 1% to 1.5% due to its supposed reduced cost structure, probably not north of 6% profit margins.

All of this has a problem of course since AMZN appears to not be in a hurry to stop the high level of capital expenditures that keep it from making any money.  If it did, Investors would be able to set proper valuation metrics for the business and the "story" would probably end and reality would likely pull that PPS down.