im travelling to korea this september...want to ask, is the food ther very expensive?

eh during september peak season right? if book those hostels or mini hostels last minute wil ex ar

haha im going to korea for 17 days in september....enough time to travel the awesome places in korea ar? i plan to spend 3 days in jeju also cos eastar is cheap...anyone can suggest a short itinerary on the 17 days ar? cos i like want to go round the island (North, west, south,east) instead of planning horribly and end up travelling inefficiently