Jeju and Hallasan --- Crampons? how much should I spend?

Hey hey -- 

Curious if anyone here has done what I plan on doing tomorrow:

- take the ferry from Busan to Jeju

- take a bus from the ferry terminal to city hall, then a bus to the Jeju bus terminal, and then finally a bus to at Seungpanak trail at Hallasan

- then, pending on a few things, either going back to Seungpanak or taking the Gwaneumsa trail down

- bus my way back to the ferry and ship back to Busan

So I'm curious if anyone else has done this, or something similar, and if they've encountered any problems or what have you. 

ALSO -- I know I need to get some crampons, but should I buy them at Hallasan, or should I go to a hiking store and buy some? The cheapest I found were 45k at the Black Yak. 

Any info would be super helpful! Thanks.