It is possible as one of my friends did it by himself. His sponsor was our university. However it is time consuming and you will bump into cumbersome stuff, which is why most of the people hire a lawyer. It would cost around $4000 ~ 5000 including the petition fees.
If you are sure your writing is logical and strong enough, you can try.
as one of my friends did it by himself. His sponsor was our university –> he had a sponsor and the sponsor paid for a couple of things.
Based on this part “변호사비도 만만치않아서” it was assumed that s/he wanted to try to do alone without a sponsor. If s/he had a sponsor, why was s/he worried about attorney cost? Also if s/he were single, s/he would not have to worry about any cost.