I got a Droid X when I got my first smartphone in July, 2010.
I was eligible for an upgrade a year later, the good 'ol days, and was intrigued about finally getting a Nexus on Verizon, so it was easy to upgrade 16 months later to a Verizon Galaxy Nexus in December, 2011.
I kept that phone for almost 2 years and was happy, but it was getting slower and lagging. I was going to purchase my next device off contract, since I wanted to keep the Nexus experience on Verizon.
In November 2013, I got a slightly used Nexus 7 for $300, since the 2013 Moto X Developer Edition was still $550-$600.
Then in July/2014, Moto offered their 2013 Developer Edition for around $345 new, tax and shipping included. I got it because of the price and the Nexus 7 was a little big to use as a daily driver.
I'd still be using my Moto X DE, if not for the Nexus 6. It was Verizon compatible. I got it from TMO and they ultimately gave me $350 that I applied to pay pay off the device, getting for roughly 50% off
If the 2015 Nexus is Verizon compatible, I'll probably get it sometime in 2016, when the price drops. Otherwise, my Nexus 6 can easily be good for another couple years.
It would probably be more expensive if I was on a GSM carrier, since they offer more choices. However, Verizon is more locked down, so any upgrade from my Nexus 6 would have to be easily rootable with an unlocked bootloader--i.e-another Nexus.