I explored this issue a while ago. It is like trying to buy a lens: high quality cannot be put in the same sentence as low cost but compromises can be found. Gadget Infinity has a couple of models for sale that are Chinese knock offs of classic Benro designs.
See this webpage and the top two items.
Gadget Infinity :: Digital Camera :: Tripod
Just be sure to get the mounting thread size that matches the screw on the top of your tripod. I bought the 3/8" one when it should have been the 1/4" one and ended up getting a bushing/adaptor that was half the price of the ball head.
Despite the low cost I have had no problems with it and it can hold quite a load. It is all metal with Nylon sleeve andit grips very nicely with almost no droop once tightened even with a bit of weight. It lives on the top of my monopod and is ideal for that purpose.