How much is my Fortnite account with Black Knight worth?

I'm just thinking about selling my account. I have: Black Knight, Twitch Prime Skins from the first seasons, Season 1 Victory Umbrella, code name ELF and Nutcracker OG version and a total of over 60 skins.

How much can I ask here on Ebay or Willhaben?

If someone buys it, it is definitely worth more than 80 euro

Not very much, at least 30 euro… Unfortunately, the ones you mentioned are too often, you can see a player with them in almost every corner. Code ELF is also no longer rare, thanks to the package where you could also buy it for the winter season. Nutcracker OG version does not exist. Black Knight is there too often. Only the Twitch package could bring you something, but as I said, only that, at least 30 euro, with a total of 60 skins, at most 40 euro.

And in general, selling Fortnite accounts is forbidden, which means that the account can be blocked if Epic Games notice it, and they notice that extremely quickly.