Vistaprint.com is doing a sale (good until May 27th) and their invites are all on sale. The ones my friend is doing for my sale is 10 for $9.99....but on sale for 10 for $6.49. And remember that if you aren't finding what you (or your host) are looking for, you can always go into other groups (save the date, wedding, birthday, birth announcements) and you can alter the words (and also add more text boxes for additional information) to make it for a shower.
The ones that I love are birth announcements for a girl but I just went into where it says "IT'S A GIRL" and changed it to "PLEASE JOIN US" and then my host went through and in all of the spaces....instead of "weight" she put the date and time, instead of the baby's name she put my name, where the length went she put her name and contact info, etc. She needed more space to write and was able to shift the other sections up by clicking and dragging them, and then she clicked on the text icon and could make a new text box to put in the address and any other information. So it turned out really cute and you would never know that it was a birth announcement!