For FD, we made him a shirt. I got an inexpensive shirt from Michael's and some paint (you can do all one color) and put handprints from DD on it.
JoAnn's and other craft stores also have inexpensive items the kids can decorate and he can display.
If you take some family photos to a service like Snapfish, you can get a collage print for him. Or you can use pre-printed photos and put them on nice scrapbook paper and in an inexpensive frame, for his office or to display in the house.
I got him a tin of flavored peanuts that didn't cost a lot but I know he doesn't buy them for himself often.
Or get a DVD he might like, and line up a friend to babysit and give it to him with a coupon for a "date night".
I've also gone to craft fairs this year to find interesting and unique items.
Some of Think Geek's shirts are on sale for $10.