My son wanted a "digger party". We are on a budget so we made everything ourselves and did the party as cheap as possible.
We made our own cakes, had "construction site" snacks, did a craft and even had a construction kit (courtesy of Home Depot).
Activities / Games
The Home Depot donated aprons and construction kits. Grown ups needed to help the kids assemble their projects but they loved it! They also had their photos taken in the cardboard background. Each child decorated a photo frame and got to take it home with their photo in it.
My son had a construction book on the table for guests to sign. It is our favorite keepsake from our parties. We also display a photo from each birthday to show how much the birthday boy or girl has grown.