Is it possible to buy modules separately?

Modules are not sold separately. There are several reasons for this.

Firstly, buying ready-made editions of the 1C-Bitrix software product, you save significantly, since you purchase modules in bulk.

Secondly, for many users, presenting the necessary set of modules as a ready-made edition simplifies the selection of the necessary product, since the name of a single module may be interpreted incorrectly by the user, and this may lead to "unnecessary" purchases.

In addition, buying modules separately will make it difficult to provide technical support in the future, purchase extensions and transitions between editions.