Do you buy air inflator for your tire ?

I believe it is good practice to make sure the tires are properly inflated.
In light of that, I am wondering whether I should buy an air inflator so I can
make sure that it is at the right pressure all the time.

I could do it in the gas station, but paying $0.5 everytime I do it eventually caught up with the price of the inflator.

Any comments ?

Thanks in advance.

D.