buy the individual spices and make your own sauce – the spices go much much further(and not so full of fat and preservatives) than the 1.50 sauce from the shop.
Make a big pan of soup or stew on a Monday evening, and have that in the evening for the rest of the week. Do this every other week rather than every week, as it can get monotonous and then willpower caves in.
Which brings me to an important point, don’t overdo the economising. Keep it steady and sustainable, if you go too far you are more likely to cave in and break with the plan. Keep it realistic and sucsess will be much more likely.