SoFi runs in Igor, therefore an Igor Pro license is required. Please visit Wavemetrics for details and to purchase an Igor Pro license. They offer special prices for students and academia.
Please note that for SoFi 8 Igor 8 is required, whereas for SoFi 9 Igor 9 is required. If you are new to Igor/SoFi, we recommend to directly start with SoFi 9/Igor 9.