Depending on your skills, most people charge about $1.00-$2.00 per envelope, so for a 100 person wedding, you would make about $100-$200 just for the envelops. If I were you, I would consider doing a per item package so that they can customize it as much as possible, but also offer a couple of packages, like Invitations, envelopes, name tags for the table and thank you notes for $1000 for up to 200 people (just an example, you have to figure out the rates). I would start at the lower end first, then build a customer base and some testimonials. Then as you get more experience you can start charging more.
As far as marketing, the first thing that you should do is set up a website. If you can't afford to have one custom built (about $1500 for a standard, static, well-designed and built site) you can use WordPress.com until you have some money to invest back into that. You can choose from templates, and update the information without knowing a bit of HTML. Keep your content up-to-date, fresh and energetic. Be sure to have a portfolio on there of your best work.
Next get business cards. Again you can do the calligraphy on them, but be sure to make them look modern and fresh which brides will look for, but use them to showcase your talent. VistaPrint.com is a great place to have them printed for a reasonable price and they make it very easy. Hand out cards to everyone. It's a fairly cheap marketing tool.
After you do a wedding be sure to send a congrats and thank you for your business note and send your card as well. Maybe you can do baby announcements as well. That's another thing you can tell them and another thing that people blow a ton of money on and after all first comes love then comes marriage.
See if you can make a partnership with websites, bridal boutiques, flowershops, baby stores and see if you put their logo or their promotional information in your congrat, thank you notes, on your website etc. then they can let you put your information in their goodie bags and do cross promotional stuff like that.
See if you can get a booth or share a booth with someone at bridal shows. That's where tons of brides get information on services. Always directing people to your website because THIS is how most people choose who they use these days which is why it's well worth the investment when you can.
Anyway, good luck!




