It's not a completely accurate picture painted, about locals receiving better service/more expert surgeons, or that foreigners can't sue so doctor's don't care about them (the government actually offers foreigners a way to address medical disputes via the Korean Medical Mediation and Arbitration Agency
http://www.koreatimes.co.kr/www/news/nation/2013/08/117_108721.html). One of the reasons why it's costlier for foreigners is b/c S. Korea as a whole, is aiming their economy's growth towards medical tourism, and to nurture international trust and to attract foreigners, they are improving safety standards, increasing governmental regulations and requirements (including registration, additional staffing, periphery services) for clinics who are catering to foreigners.
(
http://www.medicalkorea.or.kr/en/why/safe-advanced-infrastructure.jsp)
There are currently still hundreds of unregistered clinics still open for business, and to be fair, maybe some of them do a good job, and that locals do know and are okay with. But they're illegal chop shops where you are gambling with your face to save money. Also, for registered (legal) clinics that aren't aimed at attracting foreigners, they would not need to have as much governmental oversight/regulations to follow as those who are attempting to attract foreigners, so costs may be lower in those places (and while I'm not saying those clinics are unsafe, their safety standards are not ensured as much as "foreigner" clinics) (
http://medicalxpress.com/news/2015-02-korea-foreign-focused-plastic-surgery-clinics.html)
Note that the bigger picture is that S. Korea's national agenda for medical tourism isn't only geared towards PS -- the government's bigger "game" is in the healthcare industry as a whole, meaning liver/heart/organ transplants and 'heavy duty' medical needs as well as biotechnology (Samsung is even producing medical equipment and has a whole medical campus now, as their business model geared for the future is in medical equipment -- beyond handhelds/ watches/ netbooks/ telecommunications). In order for trust to be gained to attract international business, the government is very keen to make sure foreigners have a satisfactory experience in the country -- including for PS -- otherwise their 'bigger game' poising to be an international medical destination is undermined. I posted a report on medical tourism in s. korea in the 'ultimate resource ps in korea thread' for anyone interested in reading more of the current context we're in...