Samsung Galaxy S4 and HTC One with pure stock Android, however you call it are now available from Google Play Store. Currently these are available from only US store and not available in other markets yet. Samsung Galaxy S4 is priced at $649 and while the HTC One is priced at $599. Both these phones are unlocked meaning they will work on any GSM network around the world.
These Google Play editions are not yet called Nexus devices as the software is not provided Google, according to reports from Phandroid these phones are running on kernels supplied by their respective OEMs and not Google ones, that means in future also these phones won’t receive updates from OEMs only and not from Google. So the updates to these phones depends on Samsung and HTC and not on Google.
So for now, if you want a pure Android experience the best bet is to get a Nexus device.