Hiring a graphic designer and a professional printer can get pretty expensive and while they will create some beautiful invitations you can find so many options online that can help you if you need to cut your budget back a little. You can find many pre-made designs that are completely free to download and all you have to do is personalize them with your wedding details and print! Pretty simple for some lovely invitations!
Check out a couple of options I found
Love and Lavender: this is only 1 of a few they have on their site. I personally love these vintage keys.
Another one I love is from The Wedding Chicks