Putting nitrogen in vehicles tires cost from $70.00 to $150.00 and really is not worth the cost since air in the tires will do just as good as the nitrogen will.
Putting nitrogen in tires really is only worth it if you plan to race the car but just for regular road use it's better to go with free air.
Topping off tires with nitrogen costs between $7.00 to $10.00 per tire but you can add air along with the nitrogen which will be just fine.
Nitrogen in tires works better as in it doesn't usually deflate the tires during temperature changes but other than that I would just recommend using free air in the tires.