Video DownloadHelper does offer a traditional "lifetime license." Instead, they use a subscription model for their "Conversion Service" (which allows you to convert downloaded files to different formats). The official options are:
: Select the one-time payment option for "Lifetime" status. get a lifetime license for video downloadhelper
Based on your request, here is the information regarding obtaining a license for the Video DownloadHelper browser extension. get a lifetime license for video downloadhelper