Letterpress is so fun and challenging. There are several ways you can approach this stye of printing. One way is to create a design in 1, 2 or 3 color, the printer will send your design out to have plates made and then each color gets printed to create your design. The more complicated the design and amount of color the more expensive it will be because of how labor intensive the process is.
Another is to go to a Letterpress shop that offers classes, I recommend Igloo Letterpress, and build your own print out of their stock of block letters. It is a fun way to spend time with friends and learn all about letterpress and its capabilities.