We've recently started buying our beef burgers from a local farm shop (they raise & butcher their own animals) and they're the best burgers we've ever had here or in the states! I don't think they add any fillers to them, but some of their burgers do have other flavours added (like pork & apple or lamb & mint burgers). For an idea of how much the burgers cost us they're 59p each. Not quite sure what their weight is pre-cooking, but I'm pretty sure its bigger than quarter pound.
If you want something a little less dubious you may want to try finding a local butcher or try a farm shop, if you're not into making your own. Good luck!