If you are looking for a free camp spot near the airport, you should check out this place. The Tempe Recreation Reserve is a nice little park, where you can find toilets as well. You can choose plenty of spots around here or on the other side of the main road – at the Kendrick Park (there a toilets as well).
Not far from here there is an IKEA and we all know what that means: cheap food! 🙂