I booked a noticeably cheaper fare and tracked every associated cost, mostly to find out whether the saving survived contact with the rest of the journey.
It survived and by considerably less than the headline suggested, and on one leg it reversed entirely.
What was added to the fare
The line items, in the order they arrived.
Seat selection, which I paid because I was travelling with somebody and the alternative was being separated.
A cabin bag, since the fare included only a personal item and my bag exceeded it.
Priority boarding, which I did not need and which the booking process presented three times in a way that made declining feel risky.
Payment surcharge, applied by card type, which is prohibited in some jurisdictions and permitted in others.
And a charge for checking in at the airport, which I avoided by checking in online and which would have exceeded the entire fare on one segment.
The airport cost
The largest single addition and the one that is easiest to overlook.
The cheaper fare departed from an airport substantially further from the city, which is the standard arrangement rather than a coincidence.
Transport to it cost several times what transport to the main airport would have, and took an hour longer each way.
The scheduled time also required arriving before public transport was running, which meant a taxi in one direction.
Together these accounted for most of the fare saving before I had left.
The schedule cost
Less quantifiable and real.
Cheap fares cluster at inconvenient times because those are the slots nobody else wants.
A very early departure means either a night with little sleep or an additional night's accommodation near the airport.
A late arrival means the same at the other end, plus limited transport options and higher taxi costs.
I counted the extra accommodation on one leg, which was a genuine cost, and did not attempt to count the tiredness.
Where the model works well
Being fair, because it clearly does for some travel.
Short trips with only a personal item, where none of the additions apply.
Travellers who are genuinely flexible about airport and time.
Routes where the alternative carrier's fare is substantially higher rather than marginally.
And anybody living closer to the secondary airport than to the main one, which inverts the transport calculation entirely.
The reliability variable
The factor that does not appear in any price comparison.
Carriers operating point-to-point with tight aircraft utilisation have less recovery capacity when something goes wrong, since there is no spare aircraft and no alternative flight later that day.
Which means a cancellation can mean a wait of a day or more rather than several hours.
Consumer protection rules requiring rerouting and compensation exist in some jurisdictions and vary considerably in what they oblige, and the practical experience of exercising them differs by carrier.
This is a risk rather than a cost, and it is worth weighting for anything where arriving on time matters.
The comparison worth making
What I do now before booking.
Total the fare plus baggage plus seat selection at the point of booking, not after.
Add ground transport at both ends, priced for the actual airport and the actual hour.
Add any accommodation the schedule forces.
And compare that number against the conventional option calculated the same way.
On the trip I tracked, the gap fell from substantial to modest, which still favoured the cheaper option and by an amount that no longer justified the additional four hours of travelling.
The one that reversed
A short domestic leg where the fare difference was small, the secondary airport was distant, and the transport cost exceeded the saving.
I had booked it without checking, on the assumption that cheaper is cheaper.
Which is the general lesson. The fare is one component of the cost of getting somewhere, and it is the only one that appears in a search result.
The environmental comparison
Worth a note since it is frequently raised.
Emissions per passenger depend on load factor, aircraft type and distance rather than on fare paid.
Carriers operating high-density configurations at high load factors have lower per-passenger emissions on a given route than carriers with more spacious cabins, which is counterintuitive given the general framing.
Which does not make flying low-impact, and it does mean the assumption that cheaper is dirtier does not hold in this instance.
Direct routings and full aircraft are the variables that matter, both of which are visible when booking.
Changes and the real cost of flexibility
The line item that does not appear until something changes.
Restricted fares generally cannot be changed at all, which means a change is a new ticket at the price on the day.
For a trip booked months ahead, the probability of some change is meaningful, and the cost when it occurs is the full fare rather than a fee.
Which is worth pricing as a risk rather than ignoring, particularly for anything dependent on other people's schedules.
Some carriers have moved toward permitting changes with a fare difference rather than a fee, which is a genuine improvement and is not universal.