1 On average, the cost of the front differential fluid change ranges from $50 to $80. 2  The estimate includes labor hours and the cost of parts, which often range from $8 to 20 (excluding tax and fees).3  For a rear differential fluid change, the cost is about the same — $50 to $80. The estimate includes labor hours and the cost of parts, which often range from $8 to 20 (excluding tax and fees). 2  For a rear differential fluid change, the cost is about the same — $50 to $80.