Every now and then, we get a note from one of our subscribers that goes something like this: Hey guys – what's the secret to getting an exit row seat? I really wanted one on my last flight but had no luck.

More than ever, the answer that depends on which airline you're asking about. And if you have to ask, you probably aren't going to get one. Not without spending some money, anyway.

In this day and age, with airlines increasingly less inclined to giving away things they can spin into revenue, some are treating the more spacious exit row seats (which usually have more than 6 inches of spare room to wiggle around in) like gold.

Want one on Virgin America? Here, the roomier seats – 38 inch pitch vs. the regular 32 inch – are thrown into a category known as "Main Cabin Select." Sounds nice, right. Don't get excited. For that tiny bit of extra space, you're paying. How much? Well, on an upcoming flight from Los Angeles to San Francisco, coach seats are $89 one-way. For Main Cabin Select? $190.

Why so much? It's the same (rather flimsy) seat, spaced just a little further away from the one in front of it. Virgin will argue that they offer the Select passengers priority check-in and boarding, unlimited food, drink and entertainment. But can you consume $100 worth of free stuff on an hour-long flight to San Francisco? That's a lot of ham sandwiches and little bottles of scotch.

Then, on the other hand, you have airlines using using the promise of unfettered access to these tiny Shangri-Las as a carrot to lure their frequent flyers to fly more frequently. Delta used to let anyone book exit row seats any time – now, only SkyMiles members with status (and people booking on pricey, unrestricted tickets) are permitted to do so.

Still other airlines won't even talk to you about exit rows in advance, only doling them out on the day of travel on a first-come, first-served basis.

At this point, no two airlines are alike. Got to have extra leg room? No worries – Airfare Watchdog to the rescue, with an airline-by-airline how-to. The information on this chart was accurate when published, but with airlines changing their fee structures constantly, you can expect new ones to be added (and sometimes, old ones to be stepped up).