Complex sentence: At £5.5 billion (1985 prices), it was at the time the most expensive construction project ever proposed and the cost finally came in at £9 billion ($21 billion); way over its predicted budget.
Split into simpler sentences: At £5.5 billion (1985 prices), it was at the time the most expensive construction project ever proposed. The cost finally came in at £9 billion ($21 billion), well over its predicted budget.