Call 'em up. They have a phone number if you click on the contact button. If memory serves, you only needed to replace the inners and that price sounds like you're getting all four boots. Of course it makes sense to replace all four while you're doing it.

Don't forget to stock up on brake cleaner to break down all the old grease so you can get them good and clean before putting it all back together (& lots of shop rags). If you're doing the job in your driveway or garage, you might want to put down something to absorb all that drips off.

BOL