My rate to proofread (which includes checking grammar, spelling, punctuation and general flow) is $5 USD/500 words. This rate could be negotiable, depending on how correct the material is to begin with.
I am a native English speaker (US) and I have experience proofreading and editing.
My schedule is relatively flexible and I could potentially commit to between 5 and 10 hours per week.
Admittedly, I have no experience with K-pop, but I do have a lot of experience with music, generally.