AFAIK, the "Crown over N" mark is an inspection mark of the Suhl proofhouse, starting in 1950.
The gun looks like it might be an Artemis or Royal model, but condition/value looks to be in the 70%-75% range.
The best way to determine current value would be to research ONLY sold/closed gun auction websites like gunbroker, auctionarms, or a specialty auction house, for another like gun in like condition, to see how much someone has recently actually been willing to pay, as opposed to some unsold asking price,
"Krupp-Essen" = The Krupp Steel Company of Essen, Germany.
"fluss-stahl" = "fluid steel", as opposed to damascus or twist steel.