I know this is from 2009 but I still wanted to say this:
It's 2014 and Rustlers are £2.20 in the tesco near me.
500g of minced beef is around £4 (cheaper if you shop around or buy in bulk - 3 for £10 etc).
500g of minced beef will make 4 monster burgers or 6 normal sized burgers. Just add and egg and a pinch of salt and pepper, make them into patties (thinner than you think because they will shrink and rise) and freeze them on a metal or plastic tray, then transfer to a plastic bag and store in the freezer. Whenever you want a burger just cook in the oven on 200 degrees for about 15-20 minutes. Or if you wanted you could cook them first then freeze and defrost/reheat in the microwave.
6 burger buns are about £1 and you can freeze them as well. That burger cheese is about 50p for like 10 slices and it lasts forever in the fridge.
There you have 4-6 burgers for about £6, much cheaper, healthier and tastier than rustlers and takes no time at all to prepare if you do a whole batch and pre-freeze them.
P.S. You can add other flavours to the raw burger mix to make amazing creations, chilli (fresh or sauce), dried herbs, mustard, cheese, bbq sauce, tiny pieces of chorizo, curry spices. You can also obviously add any salad or sauce on top, try a chilli burger with doritos and guacamole or a curry burger with mint and yogurt served with rice.
The possibilities are endless!