I have heard people say you should never buy coupons on money because you shouldn't spend more money to save money. But in actuality, you can save more by buying more coupons, even if you are paying to get more of them. Here is how to put buying coupons into perspective.
Let's say your family goes through a dozen jars of spaghetti sauce a month. Let's say you know there is a coupon for $1 off two jars but you have already used the two coupons you had, the sauce is now on sale for $1 and you can double the coupon - suddenly that is free spaghetti sauce. So lets say you can buy 40 of those spaghetti sauce coupons for $2. That is 80 jars of spaghetti sauce - enough to last your family for several months - for a mere $2 - which would have otherwise cost you $80 without buying those coupons, or more than that if you didn't buy them on sale. So a $2 investment saves you $80+ off your grocery bill for the next several months.