If your sensei is the same Inaba Sensei that I met in Japan a few years ago at Igarashi Sensei's 20th Anniversary Seminar, then I would say your are indeed getting a good deal. The Yongsan Aikikai (member of the Korea Aikido Federation) members pay only $40 per month. They get me (2nd Dan Aikikai) for 3 classes per week. They do have the opportunity to go to classes off the US military base at no extra cost (I teach 2 extra classes "downtown" at the KAF headquarters per week). KAF headquarters members pay about 100,000Won (about $97) per month. Classes there are everyday of the week (M-F at 7am, 11am, 5pm, 7pm and 9p, Sat 3pm and Sun 12pm). Most classes are taught by Youn Sensei (4th Dan Aikikai), his wife, or one of the other Yudansha (I teach the Friday 9pm and Sat classes, Andrew teaches the morning classes and another Shodan teaches the Sunday class).
There are other dojos spread throughout Korea, but I am not up to date on what they charge.
Youn Sensei is a marvelous instructor with a great martial arts background both inside and outside of Aikido, so I have no complaints. Considering the cost of living in Seoul (its a pretty expensive place to live) it is a good deal....