Advice On Traveling Out of China! (Beijing)

Hello friends,
I have to leave China for a few days because my business visa only allows me to be here for 60 days at a time and it is now reaching that point.

Does anybody know the best destination to travel to for CHEAP outside of China? I have considered Thailand, Japan, Hong Kong, and South Korea thus far and have heard leaving the seaport out of Yantai, China to Incheon, South Korea can be quite cheap by boat. I am looking to spend less than 2,500 RMB on a round-trip.

I have also considered swimming but I don't think it's efficient :o)

Thanks!