I just got married and have 1 extra box of the Brides line invitation kit left over. I used the kit and everyone thought they were professionally printed. THe kits are $40 at Michaels. I'll sell this one unused for $25 and I included extra ribbon. So you'll be spending less than $1/invite!!!
THe kit comes with ribbon, but I chose not to use them on the invites for weight reasons. Which worked out beautifully, because even though the envelope said "extra postage required" I kept it underweight and paid the normal stamp price and the extra ribbons were used for gift wrapping and to decorate bubbles
Gartner studios has the downloadable templates, so you don't have to worry formatting correctly.