My dad (aka Papa) recently got a new job at Max's dream land: a tractor & equipment store. We went and visited Papa at work and Max got to test out the display tractors, look (from a distance) at all of the tools they use to do repairs, and check out a particularly large
For another cheap thrill, there's road construction going on near Max's daycare and it has been a fantastic source of free entertainment all summer for the kids to watch the trucks drive by.
If you also have a little (or not so little) person interested in trucks/tractors/etc, see if there's a local Big Truck Day, ask if you child can sit on the display pieces (which are usually disabled so they can't be stolen), or even find a construction site and watch the trucks work (staying a safe distance away, of course). If you have a video camera, you can even take those trucks with you. My MIL made a video for Max of all of the construction vehicles (and even a street sweeper!) around her neighborhood. Alternately, you could take photos and make your own tractor/truck/etc flip book to look at when the real deal isn't available. I have a flip book on my list of things to make Max... I know what I'll be taking pictures of this summer!