Here is the honest account of my worst budget travel mistake and what it cost me, because the failure modes are instructive.

I was doing the classic Balkans route and had 3 days to get from Sarajevo to Athens for a flight home. I found a 'budget' overnight bus that would get me there with an 8-hour layover in Thessaloniki. Cost: €35. I didn't research the operator, didn't check any reviews, booked it because it was cheap.

What happened: the bus was a legitimate service but it broke down outside Skopje at 2am. The company put us in a basic motel for 8 hours and sent a replacement bus. I missed my Athens connection window comfortably, arrived in Athens the afternoon of my flight departure, traffic got us to the airport 45 minutes before the flight (Ryanair requires 40 minutes minimum), and I got to the gate to find it was closed.

Cost: a new one-way flight from Athens to London the next day: €220. One extra night accommodation at Athens airport hotel: €45. Total cost of the breakdown: €265, versus the €35 I saved by using the budget operator instead of a reliable bus company.

Lesson: for transport connecting to a flight, always build in at minimum one buffer day. For any segment where being late has a cascading cost, spend more on reliability. The risk calculation for the final transport segment before a flight is completely different from any other segment.