When you install the SMP Workflow Solution, there should be a page in the solution where you can download the Workflow (tool) installer. If I remember correctly, it's Manage - Workflows - Download Workflow Server and Designer.
Yes, the tool is largely free, we just "hide" advanced featured based on the license level of the SMP WF license (for 7.0 SP2). For 7.0 SP2, using a trial license may prevent you from getting access to some advanced component generators. Component generators should be a lot more open in 7.1.
More and more solutions are getting released with some "pre-built workflows". Maybe this is what they mean when you have to "pay for it"; maybe those pre-built solutions aren't available at a that solution's trial level. (unsure of this) But regardless of what level you get the Workflow solution, you get the doenload page for the tool, and it's free to install and play with.