Since you'd have to pay for the device and the second year at maybe $70/month, maybe it would be more cost effective or something to consider Virgin Mobile $45 plan (or the $35 plan if you dont use many minutes) or Straight Talk etc.
I'm thinking of the taxes and fees Sprint tacks on which can be over $10/month in some states. If the others don't add that on or include it all in the stated price maybe that's better.
In regards to the second year, you're not obligated to stay a second year. So in terms of it being cost effective, I think of it as just 1 year at $10 per month (that is what it costs to upgrade to unlimited data from the free plan that only gives you 1 GB) and then you can choose to stay or leave. With that in mind, the taxes you will be paying will be based on just $10 a month so I imagine they will be fairly small. In addition you have to pay a $30+ activation fee and whatever other monthly fees sprint tacks on to a bill. Finally, you have to buy a device at the "student price" and I will be getting the Nexus 5 at $450.00, plus taxes on that purchase.
So if I have it correct: $450.00 for the device, taxes on that purchase (my state should be around $31), $120 for 12 months unlimited data service, around $30 activation fee, small amount of monthly service taxes (my guess is $40), and whatever the service charges are. The last number I have no idea, so I'll say $50 for the year. A fairly liberal guess of Total = $721. If anything I'm guessing it's lower.
So, I definitely could have done my math wrong and/or forgot something in my calculation, BUT if I'm right, that is a pretty good deal for a year of cell service with unlimited data and the ability to walk away to do as you please with a Nexus 5.