I believe it cost around $7-$9 a quart online. I purchased it from a store and they way overcharged me. Changing the trans fluid all depends on your driving habits. I hope we are all talking about manual transmissions. 15,000 miles if you race and beat the hell out of your car, 30,000 miles maybe, maybe never again. I don't really know. I changed to MT-90 at around 70,000 miles. I wish I had done it sooner and I probably will change it once more (I have almost 3 quarts left) before I move on to another car. Damn Steven, you beat me too it.