When considering alternative airports, you alone must decide how much driving is practical for you. Is a 200-mile radius too large? In some remote locations, a 200-mile trip to the airport is the norm. But for other travelers and circumstances, that circle will need to be drawn much smaller.
Should you draw a similar circle around your destination city? Some people are willing to drive after arrival, and as we've seen in some of the examples, it can pay off handsomely. Generally, travelers make the destination circle a bit smaller, but you should adapt a strategy that fits your travel situation.
It never hurts to ask about the alternatives. Factor in that limousine ride or the parking bills before making a final decision. If the resulting net savings is only a few dollars, you'll probably decide an alternative airport is not worth the trouble.
In online searches, simply look for a box that says something like "check other airports" and click it. Such a mechanism is standard in all search engines. Taking the time to find out will help you make an informed decision -- the goal of every budget traveler.
