Qlik Sense Desktop - free
Qlik Sense Server - By itself, the server is free. You can set up multiple servers(nodes) in the same site Qlik Sense (analogue cluster QlikView )
But to access it you need to purchase tokens.
1 token = 1 user access pass (unlim document, unlim time, 5 concurrent sessions, quarantine 5 days)
1 token = 10 login access pass (unlim document, 1 hour, 5 concurrent sessions, quarantine 28 days)
more info you can read here http://help.qlik.com/sense/en-US/online/#../Subsystems/Server_deployment_and_configuration/Content/Qlik Sense/QSSRM_Licensing_Access_Types.htm?Highlight=Access pass
Michael , you purchase 'tokens' for end user consumption or development that happens on a Qlik Sense Server. No charge for desktop.
A token can be a 'named user' or a token can provide 10 one hour logins by any user without a named token per 28 day period.
There will also be a cost to expand Qlik Cloud beyond 4 users (developer + 3 end users) but its still in beta.
To work out the proper mix for your use case you should contact your account manager at Qlik.