Naw. Just going for leisure.
No of course don't cancel your ticket.

Going to S.Korea still isn't as expensive as going to Japan, so there's that. 

If I compare prices of food, accomodation, products between Tokyo and Seoul, Tokyo still comes up to be more expensive. But then again, I've only ever been to Tokyo once and I've been to Seoul countless times. So the comparison there may be unfair as I'm more familiar as to where to get say; the same product but for a cheaper price. You know, like how a local would?

In your experience, why is Japan is cheaper though? Would love to know so I can pre-plan better to a trip there again.

Also I know that since Japan is going to have lots of tourism promos coming up to promote their country even more due to Tokyo 2020 Olympics, so here's hoping there are some great promos.

100-250 altogether for both flights? Then u can go for Jeju air la..

I got my tics for 300+ on Korean air for two flights, Seoul - Jeju - Busan.

eh? per flight? then i got the korean air also same price le..one flight is around 55k won..

the ktolleh pocket wifi then i got last time is work across korea.

The air ticket price depends on the date, time and promotion period. If with promotion, Eastar Jet can go as low as 12K won for 1 way.

In term of air line comparison it is very subjective. We can't expect much if it is budget 
Most people will always compliant for a single minor thing that is not on their expectation regardless of budget or premium. 

Then you may op for Eastar Jet or Jeju Air. Korean Air will be slightly expensive even after promotion. The different is Korea Air got 20KG baggage.

i got KT Olleh last time.

I used Travel Recommends in Seoul and Ilsan no issue

can always whatsapp them. They set up a booth at the capsule hotel there.

No need buy olleh Egg nowadays..

Just use KT sim.. Just noticed it at airport.

https://roaming.kt.com/rental/eng/product/sim1.asp

UNLIMITED DATA and no need carry another device.. and just use hotspot tethering for friends/family to use.

Kinds Period of use
27,500 won 5days
38,500 won 10days
71,500 won 30days

Thank me when you come Korea

Ask for more days la~

For me I booked only one hotel in Seogwipo after some researches and studies (online). Reasons being:

1. Don't want the hassle of checking in/out while changing hotel.
2. Will be renting a car, so don't really need the (slightly) more convenient public transport in Jeju-si.
3. Seogwipo seems to have more natural attractions.
4. Jeju-si more nightlife but if I want that I might as well stay in Seoul.
5. Got some special promotion from Agoda for one nice hotel in Seogwipo inclusive of breakfast for two.
6. Not too far to travel from one place to another as Jeju is not that big anyway (the travel seems long mainly due to low speed limit).

Anyway that's just me 

Oh ya, btw, regarding the speed limit, 60 km/h is only when you are in town/village. Main roads mainly 80 km/h.

Even if it's far, plan your itinerary in such a way that you will visit those places in a day. It's not like you need to travel between North/South everyday.

Some places like Udo Island, it's equally far no matter you stay in Jeju-si or Seogwipo.

Less than an hour by driving.

https://www.rome2rio.com/s/Seogwipo/Jeju-City

27.4 km
https://www.google.com/search?q=distance+fr...chrome&ie=UTF-8