Model paint in spray cans is ridiculously expensive. Next time you have some time to kill and you want to try out your third grade math skills, take the price of a can of Testors or Tamiya paint, and divide by 3 (the number of ounces in a typical can of "model paint") to get the per-ounce cost. Ouch!
To make matters worse, the spray tip usually starts to sputter and spatter or clog up altogether long before all the paint is used up. And every time after you finish spraying, If you follow the manufacturer's advice to clear the spray nozzle by turning the can upside down and spraying paint until the feed tube is clear and you're just spraying propellant, you're wasting a lot of that very expensive paint (not to mention all the overspray!)
The solution: Keep a glass baby-food jar filled with the appropriate thinner for the sprays you use. After you finish spraying, pull off the spray nozzle and drop it in the bottle of thinner. Next time you need to use that can of paint, you should have a clean spray nozzle ready to go!
Note: Different brands of paint may use spray tips with slightly different "throat" diameters... don't assume that a nozzle from Brand X will fit on a can of Brand Y. You might want to keep separate bottles of thinner, each labeled "Testors," "Tamiya," "Walmart," "Krylon," etc. so you can keep all the Brand X nozzles separate from the Brand Y nozzles.