Hi @Surfingsara - I originally thought we'd do printed for sure. But it IS expensive! Plus, we don't have anyone's addresses, our guests are internet savvy, and we were trying to get the STD out fast with the website and booking information. Plus we could see who opened it and link directly to our website, which we hoped would increase the likelihood that people would go to it.
I actually paid $15 for a designer on Etsy to create a custom STD as a jpeg and uploaded it to Celebrations.com. Paperless post is also really nice. They animate the email so there is an "envelope" in the email that the recipient clicks to open. Both sites have great templates you can use, or you can upload an image like we did.
In the RSVP section on our website we asked people to enter their mailing address. That way we have it for a pre-travel mailer and thank you notes when the time comes.