Withdrawing conference paper (after acceptance) due to budget issue

I'll leave a discussion of the ethics of withdrawal to someone else, but the main consequence of withdrawing your paper will be just that: Your paper will be withdrawn. It's unlikely to be something that's held against you.

It may be a slight inconvenience to the organisers, particularly if you were accepted for an oral presentation, to have to find someone to replace you (or to leave a gap in the programme) but part of taking on the role of organising a conference is accepting that these things happen.

You say that you've not submitted the camera-ready paper, so the proceedings will not have been completed. Therefore I'd suggest that there'd be no real damage done if you withdrew.

To summarise. It might be a nuisance for the organisers (one they may well have accepted as par for the course), but there's no real harm been done.

Edit: This isn't in answer to your question, but if the issue with the submission is simply financial then it may be worth contacting the organisers to ask if they know of any financial support that might be available, as well as conducting your own search for funds, before withdrawing.

No, withdrawing a paper in the situation you describe is not unethical.

By not announcing the registration fees in advance of submission, the organizers left you having to make an ill-informed decision about whether or not to submit. It turns out that you made the wrong decision but you couldn't have known that in advance, so it is not your fault.

You should contact the conference organizers. Explain that the registration fees are higher than you expected and ask if there is any financial support available. There often is.

In future, though, if you're considering submitting to a conference where the registration fees haven't been announced before the submission deadline, you should ask the organizers for an estimate of the fees.

Organisers usually expect some program changes; in this case they should expect more as they've provided insufficient information for you top make an informed decision. Conference programs often appear first in draft form. The final version often has some sessions finishing earlier than would be expected (this is particularly obvious when there are parallel sessions) as this is better than leaving holes in the program if a session can't be (re-)filled. Organiser and atendees have to accept this. There are plenty of reasons an author may submit with every intention of going, then not be able to go. A major one that's had questions here (or perhaps on travel.se) is that they can't get a visa. A conference I was at recently had a talk cancelled at the last minute when this happened to an invited speaker despite their best efforts.