its all about quantity. To shoot a pair of bike fenders wouldnt take much more than 2/3 of a paint cup for 3 good coats.
Gal of clear is like $70, hardner is like $25.
I have 3 gals or so of clear (in stock aka sitting on the shelf in my paint room) and enough hardner. I have alot of supplies, and a bunch of basecoats too, but Bimmer white i dont have on hand.