1 For example, CostHelper readers report paying $90-$378 for a transmission flush at a oil-and-lube or auto repair shop, at an average cost of $160; or $77-$295 at dealerships, at an average cost of $205; and a CostHelper reader in Nevada reported being charged $766 for a transmission fluid change on a Lamborghini Diablo. Flushing a transmission with a pressurized machine can cost $125-$300 or more, and may include pushing a special cleaning compound through the system.