We used the tool's open-source version. 

I don't have the specific numbers on pricing, but it was fairly priced. 

There are licensing fees that must be paid, but I'm not sure if they are paid monthly or yearly. That is handled by the commercial department.

We are using the open-source version of Cassandra, the solution is free.

This was for an enterprise company and they are expensive. Cassandra has a heavy pricing mechanism because it's a yearly license. I'm pretty sure we were paying something around $50,000 annually at that time. 

We pay for a license. 

Cassandra is a free open source solution, but there is a commercial version available called DataStax Enterprise.

If you want technical support, you will need to pay for it.

In the UAE or in the Gulf region, you're required to buy from a local vendor so prices will vary from vendor to vendor and region to region. We have a monthly license and you can generally bargain for a better price.

The application is open source, so we do not pay for it.

Pricing and licensing depends on what you are doing: If you are using it for major production work, I recommend that you purchase the level of support that you would need.

We use the open source version, so it's free. Costing needs to take into account home grown maintenance and support, as that can get involved.