Monday morning’s Barenaked App: The Figures Behind the Top Web Apps featured representatives of five companies that run five or so web apps, but not “the top web apps” by any form of wild exaggeration.
I’ll give you an overview of the overview: The five apps cost (in terms of money spent anyway) to build ranged from $20k to $200k and monthly ongoing costs range from $3k to $150k.
You could read the slides for a bit more detail, but you’d miss out on the folk wisdom dispensed. Guess you’ll have to wait for the podcast.