What is the difference between small teams and growing teams license for bitbucket server ?

[Vikas Mangal]

Small teams license costs $10 (one time payment) for 10 users and growing teams license costs $1800 (one time payment) for 25 users. Why there is that much difference between the costs ?

If I buy growing teams license for 25 users, can I upgrade it to more users with just paying the difference in price ? For example - If I buy growing teams license for 25 users ($1800) and upgrade it to 50 users ($3300), will I need to pay $1500 ($3300 - $1800) for the upgrade? Can the same license be upgraded or I need to get the new one issued?

[Phill Fox]

Atlassian provide a low cost entry point for 10 users for all their applications to allow small teams to get the benefits of the application at a very low price. 

As you upgrade your number of users you can upgrade the licence and your local Atlassian partner can advise on the options available to you at any time.