Hi J. -- Congratulations to your husband AND you!
Take a look at Swaravsky (SP!!) crystals. They have a good collection of them in Macy's and probably other comparable stores. They have all kinds of figures that are significant -- if not something that cries "Graduation," then maybe a crystal heart or puppy or boat or whatever her interests are. They aren't cheap, but would be affordable. Also, one would be very small -- easy to pack and very discreet to keep around ocd husband!
Paperweights can be super expensive, but a couple of years ago I found one for around $15 -- a plain, dark red glass heart that came in a handsome felt-lined box.
Or go to a good jewelry store and find a sterling silver Christmas tree ornament and have it engraved something like "To Mom - Thank you! - We love you!" and then put your names and the date of his graduation.
You'll think of something! Have a wonderful time!
L.