I am going to Beijing for 4 weeks this summer as well.  haha.  I'm bringing juice and mods and attys with me, but it'd be fun to find a vape-shop, and it'd be great to find some cheep clones.  I figure there will be some vendors selling vape stuff at the Silk-Market or the Ya-Shao market.  Those are the go-to places for cheep shopping.  Tons of counterfiets, and tons of not-counterfiets.  You've just gotta sift through some of the crap and barter for a good price.  If you're western, they will try to rip you off really hard.  Like, take a pare of Nikies.  They would be over $100 in the states, so the chinese vendor will ask you for $100.  If you are Chinese they will give you their real price which is more like $30, but you should be able to get them down to $10.  I always come back with mass $10 shoes.  If they wanna rip you off, just walk to the next booth and they'll have the same stuff.  Shopping in Beijing is awesome.  It'd be awesome to find vape stuff!