I would suggest the Moto X 2014. I have the Verizon Moto X 2014, and its very similar to the Nexus 6. The 5.2 inch display and thin bezels makes the phone similar to the iPhone 6 in height (though the Moto X is slight wider). Since it has Andriod 5.0, it makes a good Nexus alternative.
The downsides are the slightly lower specs, 801 vs 805, 2GB vs 3GB of ram, but those don't make a difference. The real caveats with the Moto X are the camera, as it only takes good pictures in moderate to good lighting, and the battery (standby time is pretty bad, but I get through a full day with moderate usage).
Overall, it's a pretty good Nexus 6 alternative. And it has Moto Maker and starts at only $500 (but I would wait until they have a $140 off promotion, which happens every couple months or so.)