In Halacha, we often find the concept of חיסרון כיס, or loss of money. חז״ל take this into account to try to prevent a loss wherever possible. For example, one may work on חול המועד if he may miss out on a large profit from a business deal.
Similarly, we are not to buy new clothes during the nine days. However, if there is a major once a year sale that will be missed, one can make such purchases.
The same is true regarding selling חמץ. Originally, this was instituted because many Jews sold alcohol. This would have meant a major loss if they had to get rid of their alcohol.
We need to make similar decisions with our Pesach preparations. We are able to lock up and sell any of our Chametz if it represents an unaffordable loss. Generally, we dispose of ready to eat חמץ in already opened packages, such as cereal and cookies. However, we are allowed to make subjective decisions to avoid חיסרון כיס.