$20 · lot of DDR - GDR stamps - sheets

I have 26 whole sheets of cancelled DDR (Eastern German or GDR) stamps. I'll also add two sleeves with un-cancelled sets. (They are neat - looks like there is 4 of each and each comes with a decorative stamp attached - athletes against war and fascism.) I do collect DDR but not sheets or un-cancelled stamps. I don't know what these usually go for and have not checked in the catalogues. These were part of a gift from my Dad and are from a German stamp dealer. I am an amateur collector.