This is called a Shadow Box Card, and is really fun to play around with. It is a simple design and you can add more layers and really make it as 3D as you want. I added two layers to this one and it looks great and I bet anyone would love to receive it. It lays flat and fits in a normal size envelope, and also stands up on it's own as well.
It is not too late to sign up for the workshop... I have a few extra supplies cut. So if you can make at the last minute let me know! firstname.lastname@example.org