Complex sentence: As a result, the French contingent started diminishing, also for economic reasons: in 1987 alone, Opération Épervier had cost France 1,700,000 French francs.
Split into simpler sentences: As a result, the French contingent started decreasing in size. Cost was another reason for a decrease in France's military presences: in 1987 alone, Opération Épervier had cost France 1,700,000 French francs.