You will need to purchase additional materials to participate in Classical Piano with Christie Peery. This is common for almost any piano or music school you join.
The materials you'll need to purchase will depend on your level and what lessons you're working on. If you're a complete beginner, start with level one. If you have some experience but aren't sure what to buy or what level you're at, you can submit a placement video to Christie Peery for evaluation once your ArtistWorks account is active.
The materials will cost between $40-$120. Some levels are less expensive (around $40) but the initial cost is in the $40-$120 range. A list of materials for each level of the school is available for members of the school.
You can find them at http://www.sheetmusicplus.com/ or http://www.amazon.com/
You can do both musical and muscular lessons without any materials. Christie has suggested that students should get started on those, as well as watch all of the introductory videos.
NOTE: One of the Workbooks Christie Peery requires has a newer version which does not include some songs currently in her curriculum (Halloween Pranks, Sakura, and 16th Century March). The old Workbook version (that includes these songs) is no longer sold and sheet music is not available for these pieces. Christie recommends that students learn these songs without the sheet music by watching the videos and by ear.