Here is a nice deal to Seoul with Cathay Pacific with prices starting at $835 over the travel period 16 February to 13 November 2017 (with school holiday periods being blacked out).
Sydney to Seoul – $858 (via Hong Kong with a 3hr layover on the way there and a 1hr layover on the return trip)
Melbourne – Seoul – $849 (via Hong Kong with a 1hr layover both ways)
Brisbane – Seoul – $835 (via Hong Kong with a 1hr layover both ways)
To book, visit www.momondo.com
Happy travel :)
From what I've seen, it's about as cheapest as it can get for a very decent layover return. Would've got this if I hadn't already booked via BYO at $600 for about 3-4 hours more on each trip.