How to beat high airfares...drive.
It takes 2 tanks of gas each way (about a 350 mile trip, 20 miles per gallon, 15 gallons per tank). The gas cost alone is close to $240. Even if you managed to burn 3 tanks instead of 4 during the trip, you're talking 45 gallons @ $4 a gallon, which is $180... and that's just gas.
The tolls are around $20 each way. So, now you're up to $220. And what about food? Add another $20 or so. More maybe.
So, now it costs the same to drive as it does to fly. And that's not even factoring in the cost of your TIME. It takes about 7 hours to drive from DC to Boston. It takes just over 1 hour by plane. Even factoring in the airport wait and transport, you're doing better... and you can do stuff while the plane flies while you can't do anything while you're driving. And then there's traffic. And the wear and tear on your vehicle.
And this is for a relatively short trip.
So, is driving really economically better? I did the math. I did the trip. It often doesn't make sense. Do the math yourself. Only for short trips does driving beat the cost of flying, and in which case, why you would be flying anyways? On the east coast, I just take the train or a bus. $20 gets you from DC to New York. Another $15 gets you to Boston. You can't beat THAT.
So, the cost of gas has completely changed the economics and argument of drive vs. fly. Flying is almost always going to be cheaper, if you can book your flight early enough to get the discounted fares.
That would be 17.5 gallons each way, not 30. The round trip is then 35 gallons, which should easily be less than three 15-gallon tanks. Even 450 miles each way fits in three tanks.
Only for short trips does driving beat the cost of flying
I don't know how much you can stick to highways on that DC-Boston route, but when I drive down to visit my parents, each way is 400 miles on 15 gallons. Even at $4.50 per gallon (and I'd likely pay a fair bit less than that after the return trip), I spend half as much on gas as I'd spend on air fare. Then there's the cost of transit to and from the airports (which I'd get hit with again in the too-likely event of a flight cancellation). I'm not sure I'd count eating as a cost advantage for flying: I can pack a lunch in the car if I want to eat cheap. The only advantages of flying are saving three hours of travel time in each direction and having a couple more hours when I don't have to pay attention to anything in particular (I can read or sleep instead of watching the road).
Next time you do the trip - calculate the cost. You'll see it's closer to the best airfare you can get on that route than you might think.
If you prefer to fully-load the airport commute and wait time, then you can equalize the time cost. And then you'll be comparing the actual costs against the benefits. I've found that the driving cost even not factoring in time and food / other stuff, is remarkably close to the airfare.
And don't forget the tolls. That adds close to $40. Blame the NJ Turnpike for much of that.
You've ignored the costs (both monetary and opportunity) of renting a vehicle or using public transit while in the destination city as opposed to having your own vehicle there. You've also ignored the potential harm of being confined to a cabin with scores of people who might be carrying airborne pathogens. You haven't considered the emotional cost of being subjected to an invasive search at the airport, or the stress of getting to your gate on-time.
To be clear, I am not anti-flying. I just think it's a sad state of affairs when it's more economically rational for a single individual to drive 450 miles each way than it is to fly. Get a more efficient car, add another person or two, require some bags, or plan an extended stay, and anywhere within a 12-to-24-hour driving radius becomes an economically irrational flight.
Traveling with a family on a fairly short / medium-haul trip (no overnight stay necessary) with lots of baggage? Driving will trump airfare costs for certain.
In the case of trains, it depends very much on where you are and where you're going. For example flying between basically any two European capital cities is almost always cheaper than taking the train.