Print-your-own!
There are 6 cards for tablet weaving per page (also known as card weaving) and a shuttle for holding the yarn.
the price is a one-timer and you can print out as many as you need (just use morals and don't abuse them for anything commercial) printing a lot for a classroom to spread the word of weaving is just fine.
card/tablet weaving is a great way for beginners to weave designed bands/belts. it is also double weave and will produce a really strong band.
A good start is to print out 4 pages on thick card stock paper, (can be as thin as an index card as well but for multiple uses thicker is better) then cut them out and thread with strings.
there are two files you will recieve, a pdf and jpeg.
follow a project on one of the many tutorials available online.
here is a great website for instructions:
http://www.earthguild.com/products/riff/rcdweave.htm