From the serial number list Volume 15, Issue 3, Double Gun Journal page 88 your gun is from 1900-1901 production. Without being able to see condition I wouldn't care to guess value. Sounds like it is a field grade which the Knock-Abouts were designed to fulfill. I would be surprised if it got above $1800 though. The gun doesn't have Nitro Proof (which didn't exist yet under the German proof rules) so be careful with pressures.