im currently spending almost 10k for 19days S.Korea-Japan trip alone, DIY trip.
Not a single regret..

Seoul -(KTX bullet)-> Busan -(Ferry)-> Kyushu (Fukuoka, Oita, Saga) -(Fly Peach)-> Kansai(Kyoto) -(express train)-> Hokuriku (Fukui, Kanazawa, Tateyama, Toyama) -(express train)-> Chubu (Nagoya, Shizuoka) -(Shinkansen)-> Kanto (Tokyo)

2 countries, full of adventures esp on land i cant speak their language