Elon is undoubtedly great at getting folks to commit money and talent to his companies, and talking about plausible-ish things like becoming a multiplanetary species is one way he accomplishes that.
"Dying on Mars, just not on impact" is Musk's final bucket list item. Almost everything else he does is to enable that vision, either directly by creating the tech, or indirectly because he knows this is expensive.
He may well fail, nobody's ever done this and we don't know how many surprises there will be.
But the ship working well enough for $200k tickets is plausible.
(The idea that banks will give people loans for that, not so much: without multi-planetary trade, nothing that happens on Mars can repay a debt on Earth, and I don't see Mars as having any special economic benefits to make such trade worthwhile).
It's certainly a gamble that there will be a million people willing to spend $200k to do this, which… well, I think it's not entirely impossible, as the idea was something I liked until Musk's own personality put me off the idea of being stuck on a planet with only his sycophants for company.
Which is a bit of a shame, but still, I'd give it 50-50 odds of being a product-market fit just for that.