You won't be using nearly at much as you think. Once you figure out exaclty how you want to use it and then use it you may only be a few ounces into it.
I'm not saying don't buy the quart...
I ended up with the 16 oz and really maybe used a few ounces on my torso, cod piece and feet.
I buy by the gallon. Better pricing that way. If there are other people in your area, you could always divide the larger quantity and you will save money all around.
And just to kind of sort of add to the conversation, I emailed ADM Tronics (Maker of Pros-Aide) and inquired about ordering directly. Yeah, not worth it. It was actually cheaper to pick it up from the local distributor where I purchased it. Still scratching my head on that one (Gonna be pissed if they're cutting it)...
That depends on your distributor, some of them dilute, but very few. Mostly the difference in price comes from the fact that they buy it in 5-55 gallon containers and repackage.