You can install a demo version without paying. When you buy a license, it is per server with unlimited clients. So your client may have 10 terminals running the software, but you would buy a single license for this application.
FactorySQL is also sold on a per server basis to your customer. Each installation that you wish to activate requires purchasing a license.
FactoryPMI can be used without FactorySQL.
You might consider our free Integrator Program if you are a systems integrator. This entitles you to a discount on our software to mark it up to your customer.