I have been so excited to start working with some letterpress items! I can't even begin to tell you how much fun this is...
I had studied printmaking and intaglio in college and loved the way you can manipulate the textures, colors and layout when working with inked plates. Let me tell you - this is a great way to get a very customized look and each piece is a bit different from the last.
You don't need to spend a lot of money to get started. After you have your initial tools, contact a local printing press (one that specializes in letterpress invitations is the best!) and see if they are willing to give you their scrap paper and left over ink. Some printer will charge a small fee, but others will give these things to you entirely for free! Just make sure they know that you are doing this as a hobby, and not competing for their business.
Here is the first set of flat notecards I was able to produce (it took a few trial runs to get the right amount of ink, pressure for embossing, and making sure the layout was correct).