Years ago our high school cheerleaders did this, selling carnations that we could buy and fill out cards for and they would deliver them- Carnations are less expensive and do fairly well not being in water all day-
I did this w/ the PAC when my kids were in daycare. We put out an order form that had to be by a certain date, with how many they wanted and the names of who was to receive it.
We bought carnations and a group of us wrapped them in tissue paper, and tied the card (which we printed out) on w/ ribbon.
It did pretty well b/c carnations are cheap, and anyone can spare a dollar- and would probably RATHER just spend a dollar than having to go shopping and spend more.