Complex sentence: Upon Löbel's death in 1799 Franke sold the rights to publication, which at the Leipzig Book Fair on 25 October 1808 were bought by Friedrich Arnold Brockhaus (1772--1823), for the price of 1,800 thalers.
Split into simpler sentences: Upon Löbel's death in 1799 Franke sold the rights to publication to Friedrich Arnold Brockhaus (1772--1823). The deal was made at the Leipzig Book Fair on 25 October 1808 for the price of 1,800 thalers.