A bus ticket from coast to coast can be as low as ~200 (NYC to Los Angeles in Jan on Greyhound) if you book in advance (apparently tickets can be purchased with cash from multiple vendors). In California (and maybe other states?) homeless people are able to make a little bit of money taking recyclable items to the refund processing center, they aren't always entirely disconnected from money.

And of course they'll stay in California. The transit systems often have no enforcement at all and allow them to freely get around cities. There are already services for large homeless populations. The police don't generally do more than say "go away". They probably know somebody in the community who is already here. And the people who live there are unfortunately so used to the stuation it's unlikely anything impactful will ever actually be done about it.