Just remove the price display for the free lifetime plan and for all they'll know it's just a category of some sort. You can remove the price by setting "Price display of plan (default: [AUTOMATIC]):" on the Presentation tab to the below or "_UE_BLANK".
Alternatively you can use CSS to try and hide the display, but this could mess with the fact the parent needs to be selected and active to be able to subscribe to the child plans. Could make auto-selection of parent fail, but can't say for sure as have not tested this usage.