You can try finding deals online, I know sometimes arts and craft stores such as michaels have random 25% off sales. Try retailmenot and slickdeals for online coupons and deals. Also if you have a student ID many stores have a discount, like 10% off. Pearl paint, Utrecht and dickblick have this.

Also maybe putting up a flyer at a nearby university or college to buy partially used paper. Lots of students don't use up supplies and end up tossing them after the term if they decide to go into another field.

Or you can make your own and press it. Screen material is cheap, 4 pieces of wood for a frame, and bricks or books for the press. You can get the raw materials from old paper scraps.