I don't know what exactly Harold Camping/FR spent on that doomsday prophecy campaign, but I want to say I heard it was over $100 million. When you have thousands of people on the streets, many of whom were not locals and needed hotels, travel expenses, etc., a massive billboard campaign (biggest nationally I've seen yet for anything religious), and cars/buses with those "ad-wraps" on them, it adds up pretty fast.
So, given the fact that they have sold their crop of three stations recently for around $80 million, that leaves only $20 mil to scrounge up to cover "Harold's Folly". Chances are, they got most of that in "special" donations anyway.
So, they can get themselves financially solvent and probably come a little bit on top, while still keeping the faithful FR listeners on AM. And the secular listeners get another station to complain about...Win-Win for all!
Radio-X