In that context think of this this way, if cost of converting methane into heat is 1 currency unit per joule of heat produced, fusion is hundred times as expens

In that context think of this this way, if cost of converting methane into heat is 1 currency unit per joule of heat produced, fusion is hundred times as expensive but produces a million times more heat so the cost per joule is one ten thousandth of the cost from methane.