Just realized my $18 hostel mistake in Lisbon cost me $140 in the end

Two summers back I was in Lisbon and booked the cheapest hostel I could find at $18 a night, figuring I would only be there to sleep anyway. The place was out past the airport in a neighborhood with no metro stop, so every single day I was paying for a taxi or a bus just to get into the city center where anything was. After four days I added it all up and realized I had spent about $140 on transport alone, which was more than the difference between that place and a $45 hostel right in Baixa would have been. The worst part was losing two hours a day sitting in traffic when I could have been walking around. I ended up moving to a pricier place for my last two nights and it was honestly cheaper overall once I stopped paying to leave my own neighborhood. Now I always check the transit map before I book anything, even if the room costs more up front. Has anyone else done the math on a cheap stay that turned out to be a bad deal once you added the travel?