The usage of video endoscopes in cystoscopic interventions of the urinary bladder impedes an intuitive navigation. Although image-based solutions such as panorama images can provide extended views of the surgical field, a real-time 3-D navigation is not supported. Furthermore, the integration of common tracking systems in ambulant clinics is often hindered due to low usability and high costs. Thus, we discuss in this paper a first low-cost inertial navigation system. Our evaluation results show that in spite of lower sensor accuracies, mean errors between < 1° and 4° are achieved for solid angles. Using endoscopes with different view angles we apply an extended endoscope model for an adaptive displacement correction. Furthermore, we implement a first guided navigation tool for tumor re-identification in real-time.