Complex sentence: Titanium disulfide was a poor choice, since it has to be synthesized under completely sealed conditions, also being quite expensive (~ $1000 per kilogram for titanium disulfide raw material in 1970s).
Split into simpler sentences: Titanium disulfide was a poor choice, since it has to be synthesized under completely sealed conditions. This is expensive (~ $1000 per kilogram for titanium disulfide raw material in 1970s).