My only suggestion is change how the price grows, you can add a few cents or dollars each extra user, because if I have 50 users I won't pay some more dollars to add the 51th.

Another suggestion is to reduce the price per extra user as it will growing like, the first 20 users costs 0,50 cents each the next 20 costs 35 cents each, this kind of thing.

It's just a suggestion, but the site is really very appealing to the eyes and the application looks like very intuitive.

Congrats!