Complex sentence: Along with Elvis Presley, who was at the same time GI, he wrote the song Mississippi River, the single was never released, but was later sold for $30,000 in 1996.
Split into simpler sentences: Along with Elvis Presley, who was at the same time GI, he wrote the song "Mississippi River". The single was never released, but the rights were later sold for $30,000 in 1996.