I just checked and found 4 which had been sold on eBay.co.uk (the most likely eBay site to find it as it was marketed by the UK licensee Marx toys) since early August 2018 varying in price from £25 to £40 (the latter was a complete set 1728/2 with box, used). All these had the original helmet, unique to Marx toys. The helmet alone sold for (under) £10 and £6.66 in a couple of other lots. The recent set 9237 is quite a lot different from the Marx toys version, but available for more reasonable prices.
I wonder why this figure sells for so much; yes it is a unique colour for the era (all body parts are dark blue, apart from the head), yes it had a unique hat (without the hat, it sells for a lot less), but it had fixed wrists. And some of the Marx toys production quality back in 1978-80 (that's a guess) when it was produced was not up to German Playmobil's standards at that time, let alone today's standards. Marks toys klickies often had 'printed' faces where the features were almost 'melted' into the face, most unattractive.
So yes, it seems to be desirable, fetches higher prices than many later Exclusive figures now fetch, but it's a bit puzzling why it's so popular, IMO!