Ahhh yeah, SubscribeStar like patreon would require one to simply stay a subscriber, or resubscribe everytime there is an update. In which case ether way one would definitely spend more than the sale price. There might be a workaround depending on how well SubscribeStar keeps track of Subs/former subs like how I think patreon can...
Is the Mac version at least available via Steam? I often see games on Itch that have Mac versions that work fine and are updated with each update. Yet are not available via the steam version.