For watercolor paper one of my favorite hacks when I want to practice is to buy one or two large individual sheets and then use the fold in half and tear along the fold method to break them into smallish card size pieces. I find I can get a decent supply of quality paper at a more reasonable price than buying it in book format and the small size (I usually go for something in the 5x8 vicinity) is less daunting to me while still being large enough to practice composition and new techniques.

I have also found that most of the chain craft stores have coupons they will send you (Michaels typically does 40% off one regular priced item) which can be handy if you are looking to buy a larger item (such as a block of watercolor paper or some kind of specialized tool).