I'm thinking of spending a few days in Korea in September, or maybe later this year. Anyone got any insight on cost, agents, etc. in Seoul for a Chinese guy? Know a little Korean (not fluent / native but can communicate).

You can try some of the full service nuru massage shops, mostly around Gangnam. Try looking at the Global 141 site for shop names that are Asian friendly, and can communicate basic Chinese or English. Day shift girls start at 11am-6pm, night shift 8pm-5am. They offer 1on1, 2on1, 2 or multi-shot relays, and open Club space (you can see other punters with their own girls, but no sharing). 1on1 230k won course (foreigner price) is 30min nuru then 30min FS, in a private room.

250-300k won Outcall agents are hit and miss, if you find a reliable agent let me know.

Goodluck!

Do you have any friends in the area?  Seoul P4P scene can be incredible if you have an in, and it really helps to have someone fluent with you to set things up/convince people you're an okay guy.  Even casual acquaintances may be willing to help out, since this kind of entertainment is widely accepted as standard for men.  Otherwise, if you're trying to set things up in a foreign language, you're probably going to get hit with some pretty steep foreigner surcharges.  

If nothing seems to be working out for you, check out Belle in Gangnam.  The proprietor there is okay with non-Korean speakers, but you may not get the best experience if you can't communicate with the girls.  Cost is around 160k KRW for a (surprisingly good) massage and HE.  No FS.  Gangnam also has a lot of other options ranging from the spinning barber pole hand jobs to anma like mentioned by the previous poster.  

Also, if you're decently attractive and outgoing, give Tinder a try.  You may be able to score a date with a civilian.  If they're on Tinder in Seoul, chances are good they'd be okay with meeting non-Koreans, and being East Asian is in your favor.  I'd start looking/chatting a few days before your trip, since it can take some time.  Some girls will flake on you once you actually set foot in the city, but every now and again...  Recommended only if you have dating app game and don't mind a bit of a challenge, though.