I am the 'official' invitation maker in our family and just got done making 140 invites for my cousin's wedding. Whew! What I have done in the past is buy the invitations from Michael's and then jazz them up. The brand at Michael's is Gartner - there web site is here:
www.gartnerstudios.com
I buy them one box a week and use a Michael's coupon, so they are inexpensive and even if you don't do anything to jazz them up, they look fantastic. If you do decide to jazz them up, just remember to keep it simple. You want to be able to re-create the invite and have it look just as good with the first one as well as the 101st one.
Can't wait to see what you do!!