I made some for my SIL a few months ago. To keep price and time down, I printed the inside information on plain white cardstock with my laser printer. I use Domtar brand which is sort of equivalent with the paper so popular from Walmart -- very cheap. About $15 for 250 sheets. Each sheet yielded two card bases which I cut lengthwise.
Then I pasted fronts on using SU papers and used a cute dollar stamp. (I made 24 invites and only used 6 sheets of bashful blue, 1 1/2 sheets of certainly celery and about 20 sheets of the cheap white.)
My MIL had given me $25 for supplies, so I even made thank you cards the same way to give my SIL.
Here's the link:
Sweet Pea Baby Shower by askagain at Splitcoaststampers
Have fun and share what you come up with!