There are a wide variety of resources at Alice.org that are free and can get you started. You will also find different textbooks listed there. I do not think your students need a text, but it might be useful for you to have one as a reference / resource.
Alice 3 has more engaging graphics, which might suit your purposes, but You may find Alice 2 more accessible and it has a built in tutorial.
I will also be happy to answer any questions you have
dslater@andrew.cmu.edu