In the winter sometimes fresh produce is expensive. You can use frozen veggies. They are generally flash frozen at the source and may actually have more nutrients than “fresh” vegetables that have been sitting in nitrogen filled refrigerator containers for six to eight weeks.
Another option is vegetable juice. Here in the States it is very cheap because it is a byproduct of vegetable canning. At about a $2.50 for a half gallon (1.89 liters) that is a lot of nutrition for your money. Forget V8 or the other name brands. Buy generic and add a dash of pepper, tabasco. lime or lemon juice.
If you are buying fresh produce then buy cruciferous vegetables like broccoli, cauliflower or kale instead of iceberg lettuce. Lettuce provides some of the least nutrition per dollar spent. Don’t forget your orange veggies: carrots, squash and sweet potatoes.