Let KAYAK do the searching
Based on KAYAK hotel searches, the most popular destination is Osaka (87% of total searches to Setonaikai National Park). The next most popular destinations are Hiroshima (8%) and Kobe (3%). Searches for hotels in Beppu (2%) are also popular.
KAYAK users have found double rooms in Setonaikai National Park for as cheap as $11 (Osaka) in the last 3 days. The average price is $256.