These Germany copy Stradivarius can be very valuable. Many of these do have some age and date from 1890-1920 and were made to be of the quality of Stradivarius so their craftmanship was high. If there is no other luthier name attached (some signed their name but many did not) the value can range between 200.00-500.00 most of the time. However high end instrument auctions have also brought 1000.00-1500.00 for some of these that are of the highest quality.
These violins really need to be assessed on site. If you are near an auction house of these masters copies, calling and taking it in for evaluation is the best gauge of their value.
International string instument auction houses, Bonhams, Bromptons, Christies and Sothebys will make appointments if you are in one of their many office regions around the World. Skinner in Boston will evaluate material if you are considering a consignment and are one of the best, XXXXX XXXXX the best venue in the US. Lastly, a local violin shop may also be a good gauge of whether this is one of the high end examples. Check your local directory and see if there is one not far that either rents, builds or sells violins..or all of the above. These shops are great resources too.
All my best, Dori