Jeju-do is popular among honeymooners and vacationing Japanese, which means that hotel prices are higher here than on the mainland, especially during the summer high season and during holidays. If you're planning to visit during those times, be sure to make reservations well in advance. Weekend prices are a bit higher, too. Luxury accommodations are centered in Jeju-si and Seogwipo (which is home to the newer, more modern resorts), but there are some lower-end minbak (private homestays) and pensions scattered throughout the island. The condo-style pensions can be reserved in advance, but the minbak generally operate on a walk-in basis -- again, not a problem except during high season.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.