Hi, I am a UK citizen living and working in Korea with an E2 visa

and ARC card which expire in November. I want to visit China on my way home from Korea. Do I need to apply for my visa before May to ensure I have the required 6 months remaining validity on my ARC card, will the visa even be valid for that long and what is the price for UK citizens? (I'm pretty sure in the UK you pay around 85GBP)...? Thank you!!