As others have mentioned, the development phase is the most expensive due to the time and effort from the design generation stage. Additionally, during the development phase, any pre-clinicial trials or clinical trials may cost up to more than millions of dollars. It takes money to find animals and human subjects to test the medical device on as well as monitoring the safety and efficacy over a certain period of time. The development phase is the longest phase which makes sense as to why more money would be put in during that time. Finding the right parts from vendors to make the optimal product requires quite a bit of research and innovation, which takes time. As well as once the product has been made, the money put forth during the 510k submission as well as PMA, and IDE continues to add more procedures which adds to the cost.