If they are not covering your travel and lodging expenses then, in my opinion, you would've be well within your rights to remove yourself from the project. In the UK, that would be against voluntary employment law (presuming you're not being paid). If they have failed to provide you with the relevant information – or your agent has failed to relay it – then that is their problem. They don't sound like a very professional outfit.
Which brings me to my second point: these people sound like disorganised amateurs, and even if they're not, I'd hardly worry too much about being blackballed. I've had many people flake on me over the years and I've never had any means of blackballing them, even though I'm fairly involved with the indie filmmaking scene in London. Yes, if someone brought them up I'd probably mention that they bailed on my production, but I wouldn't/couldn't go out of my way to do so. I think at the low-budget/indie level, getting blackballed is a bit of a myth. And it's a dangerous myth if it persuades people that they are somehow obligated to get involved in bad or inappropriate projects, just for fear that they won't work again. This project sounds like a bit of a shocker and, in my opinion, unless they are willing to arrange transport for you and put you up in their city for the duration of the shoot, you should probably drop out.
I think Rik offers good advice and a good line in sucking it up and being a better professional than them. But (perhaps for the sake of others reading this who find themselves in similar positions) I think it's important to reinforce that your employer has obligations to you. Simply saying that you'll work for someone doesn't mean that they can ride roughshod over the law and/or basic decency. I think that, if this question had been asked by someone other than h44, they might have received a slightly different answer. Just as you should be providing a suitable work environment for your actors when you're producing (as 1000s of words have been expended trying to persuade you to do), you should also expect a suitable environment from producers when you are acting.
