Should be no more than about $5 a tire. That's the most I'd pay for the Sprinter or a passenger car. Might be more than that for truck tires, but I'd shop around, 'cause if it's much more than $5 even for a truck tire, they're charging too much (for a passenger, Sprinter, light truck, the nitrogen costs them about $0.40 a tire, for trucks probably $0.60). Most places that have it, put it in for free when you buy the tires, and will usually not charge anything more at rotation time for it.
Dunn Tire, Bell Tire, Tire Discounters, Costco. I keep hearing about truck stops, but I dunno.