Costs for Open-E JovianDSS are plain and simple: license only what you really use. The licensing system is based on the capacity of each storage environment, and designed to be as fair as possible for users. You license only the usable capacity for mirrored arrays. In case of arrays with single, dual or triple parity, the license counts all disk capacity in the array but without cache and spare disks.
Open-E JovianDSS is not compatible with Open-E DSS V6 or V7, as it uses a different file system. Please be aware that for this reason an update is not possible, and make sure to choose your product according to the functionalities you require.