Feeding a family: conventional or organic?

Say you are a mother and you have four kids. One is 16, the other three are 20, 21, and 23. All of them are still living at home. 
Now you only have a set amount of money to spend on groceries every week and it's not much. All of your kids except the oldest, your 23 yr old son, are students so they don't work. Your son was raised with the help of your mother and never learned to equally participate in cleaning, cooking, helping out with dinner (things girls are usually expected to do). 
So do you buy only conventional which is cheaper at your local store and are able to have 80% of the food needed for a good filling diet for your kids?
Or do you only buy organic which has less pesticides and chemicals and have 50% of the food needed for a good filling diet for your kids?
Or do you do both and have 65% of the food needed?
*its not 100% for any of the choices because you are just stubborn about a grocery budget and feel like you don't want to spend more than what is "necessary". 

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