Displaying different options based on the selection of an option (Show more hard drives when selecting Hardware RAID, for example) is considered field logic. This is planned per CORE-1708.
The contract time could be a simple config option that adds a monthly surcharge to the base package price which you'd set for the longest contract term. This you could do now. You can also have config options for many other fields, like processor, RAM, disk, control panels, etc so long as they don't require field logic (Until we complete CORE-1708).