Skin Boat School sez 1 Oz of dye powder. They sell a couple Oz of dye for $10, enuf for 1.5-2 boats, they say.
Good dyeing instructions on their site.

If thats all you need, you can save the shipping, and go to Jo-Ann Fabrics. They stock it in 1/2 Oz bottles, on sale now for $3.35 They have more colors, too (Usually a 40-50% off coupon somewhere for them, too...)
http://www.joann.com/jacquard-acid-dyes-1-2-ounce/xprd140367/