You don't have to spend a lot on collage paper. If you look through items you already have, you will find a near unending source of paper to use in your art journal.
Some people like to add bits of paper from their everyday life to their journal. Receipts, bus tickets, concert admissions, playbills...it's all fodder for the collage in your journal.
Here are a few ideas to get you started when gathering up collage paper. I like to have a basket next to my work area, filled to the brim with magazines and books all ready for collage.
1. Magazines and Periodicals...nowadays you can get magazine subscriptions for very inexpensive. Fashion magazines, National Geographic, art magazines, magazines that stores send out with orders, home decorating and travel magazines...find some that you love and you will enjoy using them in your collage. My husband works for a magazine publisher so I get some subscriptions free...(Lucky me!). Most cities also send out a free newspaper to keep people in the know about things going on in the community. Newspapers are a great source for collage elements as well.
2. Phone books...Again, another free source of collage paper. You could actually create a wide variety of paper crafts with a phone book alone!
3. Music books and notation...If you have been into playing music at any time in your life, you will probably have a collection of music books or tablature to choose from. Music notation can be so beautiful in your art journal, you can choose notation from your favorite songs to create a visual soundtrack in your art journal.
4. Adult coloring books...these are a great source of collage paper! I color in the images with permanent marker, or just use the black and white paper for collage elements in my works. You can also find really cheap coloring books at the dollar store in your area, another great source for collage. Try to find books with a bit thicker paper so it will stand up to the glue you are using.
5. Fiction and Non fiction books and textbooks...I collect books and have a habit of tearing out random pages for collage. Then later I always wonder which pages are missing when I go to read them again. So if you use books from your personal library, be sure to choose one or two and write on the cover "for collage" so that you will know which books are missing pages.
6. Junk mail...junk mail provides an endless free source for collage. I don't tend to use junk mail much but some people love using it in their journals.
7. Scrapbook paper, origami paper and other decorative papers...last but not least, you may want to add some beautiful decorative paper to your collection. Origami paper is really inexpensive and you can find great bargains on it. Scrapbook paper is another option and a pad of scrapbook paper can go a long way. The paper is relatively thick so you can use it in a lot of different mixed media projects as well.
Have fun sourcing some papers, and I challenge you to look in your own home before buying new. Use paper that has some kind of meaning to you and your art journal will take on a whole new element of depth.