Amazon finally has an official listing for Sprint 16GB (contract and off-contract price).

http://www.amazon.com/Google-Nexus-5-Black-Sprint/dp/B00GCLZJ1G/ref=sr_1_13?s=wireless&ie=UTF8&qid=1383903068&sr=1-13&keywords=%22nexus+5%22

$499.99 is the price off-contract.

http://www.amazon.com/Google-Nexus-5-Black-Sprint/dp/B00GCLZJ1G?tag=androidcentralb-20&m1k=d_ac

and before anyone asks:

There is NO LOCKED NEXUS 5 The Sprint one is EXACTLY the same as the play store version Amazon only sells the 16gb black