SSH& is an organization that offers quite affordable rooms for students in and around Nijmegen and Arnhem. They own 25 student-complexes and 80 houses, which together account for more than 8,000 rooms.
You can sign up for SSH& the first of November a year prior to the start of your study. To do so, you only need to pay €20,- once for the entire lenght of your study. As a first-year student you get priority in four complexes in Nijmegen; Hoogeveldt, Vossenveld, Galgenveld and Leeuwenstein. From the first Thursday of July on, you can apply for rooms via their website.
More information about SSH& can be found here.