If you're looking to learn Korean in Seoul, the university programs are the most established option. Seoul National University's LEI is the most prestigious with competitive entry, running about 1,730,000 KRW per 10-week term, while Yonsei University's KLI is known for excellent textbooks and a rigorous curriculum at around 1,830,000 KRW per term. Sogang University's KLEC is the best choice if you want to focus on conversation, with smaller classes at about 1,780,000 KRW, and Ewha Womans University offers a well-structured course on a lovely campus for around 1,680,000 KRW. Korea University's KLCC gives a good balance of skills at about 1,750,000 KRW per term.
If you're on a budget, there are great free alternatives. The government-run KIIP (사회통합프로그램) is completely free and even leads to visa benefits, the Seoul Global Center offers free Korean classes, and many community centers (주민센터) run free or cheap classes in your own neighborhood. For self-study, Talk To Me In Korean (TTMIK), the King Sejong Institute Online, Duolingo, and YouTube channels like Korean Unnie and Miss Vicky are all worth trying. A practical path many people follow is to start with KIIP for the free classes and visa benefits, then move on to a university program later if they need more.