I have a friend who is a teacher and I always ask her what to get my kid's teacher's. She continually says that gift cards are the best thing she gets because she can buy things for the classroom. Perhaps you can go to the principal and ask if there is anything the teacher has been requesting for the classroom.
I know my friend is always looking for new books, and other teaching tools for her kids.
Also, this year she told me to get some of those candles at Bath and Body Works...they smell amazing and I want keep all the candles I bought as gifts!!! Perhaps you could put together a small "side" gift like that to go along with a gift card...my friend usually likes those Visa cards because she has a choice as to where she can use it.
There is always the spa. Pedicures and manicures are always welcome! It would be a nice relaxing end to the school year and a great start to the summer. A simple manicure is usually only $15 or $20 and a basic pedicure is usually $35 or $40 which would leave enough left over to add the tip on as well.
$80 is a lot and can go a long way for both. I do like the picture suggestions as well. I always like to get pictures though =)
Good luck!