For my friends shower last spring, I caught tulips on sale for 50 cents each. If you check right now, you might be able to find some annuals on sale super cheap.
Then I took the pot it came in, placed it in a regular paper lunch bag. I printed out a sticker with the baby shower info, date etc. and put them on bags. I had also stamped the invites, so I put a stamp on the sticker that matched the invites (I think it was a baby bottle stamp that I got at Micheal's for a buck). Then I rolled the bag down and tied cheap curling ribbon around it to hold the bag to the pot, so the flower would show out the top.
Since they were perrennials, I had something on their about planting the flower in your own garden, and watching it grow and always remembering how the little girl has grown when you see that flower. It was cute and poetic...just don't remember how I worded it!