Math 51: Linear Algebra - Levandosky $90 - Has a little bit of writing but still is very good condition.

http://www.bkstr.com/webapp/wcs/stores/servlet/CourseMaterialsResultsView?catalogId=10001&categoryId=9604&storeId=10161&langId=-1&programId=562&termId=100025341&divisionDisplayName=Stanford&departmentDisplayName=MATH&courseDisplayName=51§ionDisplayName=01&demoKey=d&purpose=browse

Math 53: $150 - Like new. Differential Equations: An Introduction to Modern Methods and Application by Boyce and Brannan.

http://www.bkstr.com/webapp/wcs/stores/servlet/CourseMaterialsResultsView?catalogId=10001&categoryId=9604&storeId=10161&langId=-1&programId=562&termId=100025341&divisionDisplayName=Stanford&departmentDisplayName=MATH&courseDisplayName=53§ionDisplayName=01&demoKey=d&purpose=browse