Hey Josh!
Often times, the rarity index here is either inaccurate to what is shown outside of Numista. Usually, only notes 94 and higher fetch high prices, unless you’re looking at a highly collected currency like the US Dollar. Notgeld, however, is a much more niche area to focus on, hence “rarer” notes fetching lower prices. With that in mind, here’s what I found:
On MA Shops (searched: “hessische 5 million mark) of the 5 million mark: https://www.ma-shops.com/schwarzkh/item.php?id=4934
and the 50 million: https://www.ebay.com/itm/363987360350?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=9uhaw42TRIu&sssrc=4429486&ssuid=aggjlxotr_u&var=&widget_ver=artemis&media=COPY
Though probably not what you expected, most Notgeld, even in excellent condition, unfortunately is just not worth that much. Past those, I cannot find any more information, even searching on hessen.de, the official website of Hesse.
——
Daniel