quorn is okay. i prefer the cheaper supermarket-brand alternatives...tesco quorn-style burgers are 18g protein/5g fat/6g carb per 100g, and cheaper than beef burgers or similar.
or, cheaper still, and if you can be bothered, make your own veggie burgers - just throw a few tins of pre-cooked/soaked beans or lentils into a blender with some peppers, onions, tomato paste, an egg, bit of flour, spices or whatever you want. use as little or as much oil as you need, i made some yesterday using none at all. and they don't taste too bad, though most meat eaters would disagree...