Hi Beth,
I just started my own custom stationary business. And my printer contact gives me great discounts on letterpress. The price he quotes me depends on a lot of factors such as number of colors, artwork, and bleeds.
For 100 complete invitations (envelope, 5x7 invite, and response card) would probably cost about $350 for 1-color and $500 for 2-color.
I love letterpress. I think it is definately worth any extra money. PM me if you are interested. You can also check out my website at Karla Zepeda Designs
KarlaV