A typical cost of accommodations is in a rage of 5 000 to 8000 JPY (40 to 60 Euro) per person per night in Kagoshima. You also may be able to find lower cost accommodations, such as guest houses and dormitories close to the venue. However, March is a busy season in Japan, therefore, the cost will be higher. It is recommended to book your accommodations earlier (no later than February) for easier booking at a lower cost.
The registration form page also supports for booking some hotels (by JTB). In the page, one can see the the list of the hotels available for booking and their prices as shown below.
The list of possible accommodations is available, based on Hotels.com and Booking.com researched in October 2021.