Is it cheaper to fly from a different airport? On the fare screen, often yes. The second airport an hour up the highway shows a number thirty or sixty dollars under your usual one, and it's tempting to just book it. The honest answer is that the fare is only half the trip. Once you put the drive, the parking, and the extra hours back on the scale, the smaller airport wins some of the time and only looks cheaper the rest of it.
What the lower fare leaves out
Say your home airport quotes $240 and the one ninety minutes away quotes $190. That looks like a clean $50 saving. Now add the parts the fare doesn't mention. Gas both directions, or a ride you're paying for. A few extra days of parking if you're driving yourself, which at some airports runs more per day than you'd guess. Three hours of driving, round trip, that you're not spending anywhere else. If you value your time at even a modest rate, that $50 gap can close to nothing before you've left the driveway. This is the same trap as the hidden cost of a cheap fare: the posted price is the one piece the airport can advertise, so it's the one you see, and everything else gets added after you've decided.
When the smaller airport actually wins
Sometimes it genuinely does, and it's worth knowing the shape of those trips. The gap has to be big, not marginal. A $50 difference rarely survives the drive; a $180 difference usually does. It helps when the detour is cheap in time, a straight thirty-minute hop rather than ninety minutes through traffic. And it helps when the second airport is one you'd half want anyway, closer to where you're actually going on the far end, or served by a nonstop your home airport doesn't have. That last one folds in what a layover is actually worth: a cheaper fare that also skips a connection is winning on two fronts at once.
The rule we'd offer isn't "always check the other airport" or "never bother." It's do the whole sum, drive and parking and hours included, before the lower number talks you into anything. That's also why the daily email prices the airports you've told us to watch and shows them side by side instead of quietly steering you to the cheapest sticker. Some mornings the far airport is worth the drive. Some mornings it just looked like it was.