You have to be kidding!!! How RUDE!~!~
Every b-day, holiday, special day, my sister for years has sent out her own cards she makes on the computer and we always look forward to them.
Anyone can go to a store and just pick up a card and buy it letting some unknown person think of the words inside. But it takes someone special that will take the time to make an original card just to fit the person they care enough to send the card to.
I would have taken the money and thanked them for the extra cash to put into my 'real' cards and then let them know they won't know about how nice the extra money helped make the cards since they will no longer be receiving one.