The Wright Brothers also weren't asking for $5 Billion+ for a test flight. They mostly self-funded IIRC.
Every human endeavour until incredibly recently in our timeline was a self-cost, whether it be in health, time or wealth. Only in the last blink of an eye have we expected a Govt or Govt funded entity to do it for us. And it's clear they can't.
Personally I couldn't be happier that someone is trying something new. It might not be a success, but it might lead to an innovative new industrial process, or way of constructing something, or it might work.
Who cares if it costs $5billion if we can progress from it and someone will fund it? What else is that money going to do? Sit in a hedge fund? Get invested in a WhatsApp clone? What does that do for us as a society and a species?