That does seem very cheap.
I'm not a Canon user, but I have had two battery grips for my Pentaxes from eBay. The first one for my K20D was a Phottix, and reasonable brand name, but it has never worked reliably.
My second one, for my
K5, I have had about a month. It is unbranded, but much higher quality. It was also somewhat more expensive, although not anywhere near the £200 for an OEM one.
The Canon grips do seem to be a lot cheaper, perhaps because they are not weather proof and have fewer functions. The shop I got my latest grip from have Canon ones too - like HERE . They gave a good service, sent the grip recorded and it arrived in less than 2 weeks, which I thought was pretty good.
Hope you manage to get a good deal.