With ten children each, I have no idea how my grandmas financed all those high school graduations, but I can promise you that they did it very economically. People get very excited about the whole graduation thing and end up spending tons of money, but if you don’t have tons of money to spend, remember to just do your best and at the end of it all, they will be just as graduated!
Senior Pictures--When they take school pictures at the beginning of the year, I buy twice as much as usual and use them for my child's senior picture. I don't know about in other places, but around here they take seniors' pictures in tuxes for the boys and drapes for the girls. It's also a good idea to buy the CD.
Cap and Gown--If you look really hard, you can find the place on the order form where you can order just the cap and just the gown without any extra. For us, this cost about $25.
Announcements--We designed and printed our own. I looked at graduation announcements on the internet to get ideas. They won't be embossed, of course, but most grandparents and relatives don't mind. Slip a photo into the announcement and send it on it's way.
Hope one or two of these ideas help!