Rather than a cheap charger I've opted to adapt existing, quality chargers or charge straight from USB.
At home I have the Google charger with a shaver adapter. This gets plugged in when I go to bed, whether it needs it or not. A full charge will generally last all day easily (I've found leaving GPS off when not required helps a lot).
At work I have a USB>microUSB cord I bought for a quid or something on eBay. It sits plugged into my PC - although the IT policy is to disable USB ports against people bringing viruses into the company on flash cards, the power's still there. If I've been using the phone a fair amount and I'm going to be out after work I'll top it up in the afternoon using that.
I've also ordered a 2mm Nokia > microUSB converter. That one was a wopping two quid, IIRC. I'm hoping this will allow me to charge from my old Nokia N95 8GB charger, which will give me around 800 mAh vs. the USB's 480 mAh.
If anyone's interested in any of these I'll dig out the eBay URL's.