The most popular foam gun on Amazon right now is the Foam King Foam Gun, which costs just under $40 at the time of this writing (and down to around $30 when it’s on sale.) I decided to give it a try. As you can see, my project Audi TT has not had a car wash in a pretty long time. Tons of dirt is sitting atop the car, so a pre-soak is just what the doctor ordered.