Beta exam is pre-released exam. For normal exams, you have 1.5-2.5 hours to complete 60-70 questions. But for beta exams, you usually have 3-5 hours to complete 150-250 questions.
Beta exam aims to let the certificate provider to increase the quality of the questions, and thus, it costs less. Usually, for SUN, an offical exam costs US $150, however, a beta exam costs US $50 only, which is 66.67% off!.