Cottage cheese is nearly impossible to find in Korea. I've found it once at Haddon Supermarket in Oksu-dong for 15,000 won for a quart (32 fluid ounces) of cottage cheese that disappeared in a day. I've gone back to Haddon several times since then, and they haven't been stocking it.
Thankfully, cottage cheese is ridiculously easy to make. You just need white vinegar, milk, cream and salt. I've found that making cottage cheese isn't cheaper than finding it haphazardly - even at four times the price of what it would cost in the states ($4). That's because milk and cream are expensive, and 1 gallon of milk only yields two cups of cottage cheese. Also, white vinegar isn't sold in most supermarkets. I found white vinegar at the Foreign Mart in Itaewon for about 5,000 won for a quart (32 fl. oz.), but you can get a massive 1.32 gallon jug of the same white vinegar at Costco for 7,500 won. I also saw it at E-mart the other day.