That sucks. Ideally you should have a Morning After Pill / Plan B for these situations, they are delivered in anonymous packages by womenonweb and various sites; The Pill is valid for 3 years (i'm a single guy and have it, never needed to use it yet). You're situation is rough, sorry you're dealing with it; With that out the way.

I am not a lawyer, a medical expert or the like, so, please consider this as information not advice. **I may have had a female associate do this**, this what I would say

There is no cheap option, you are in Korea, you're f***. But there are options. Vietnam and India have both commonly used pills for an abortion over the counter or with a quick visit to a doctor. Book a visit with a Doctor in Korea asap, the medication you're after is Cytotec 싸이토텍 (Misoprostol )' or 'Mifespristone' ( I dont know the Korean name for this one)
Misoprostol and Mifespristone is the actual medicinal drug, Cytotec is the Korean brand. Each country has their own name for it.

Based on their advice, you'd need to take a weekday trip to Vietnam or India
Please don't just book a plane and self medicate! Good luck on whatever you decide.

(India)

https://www.womenonwaves.org/en/page/4873/india--organizations-and-clinics

(Vietnam)

https://www.womenonwaves.org/en/page/4899/vietnam-clinics-and-associations