How does 'accepted' but not published paper look on my CV?

Submitting work to a conference, having that work accepted, and presenting that work at the conference has value, such accomplishments should appear on CVs.

Withdrawing an accepted work from a conference due to no funding shows lack of foresight, perhaps even disrespect (by wasting time), and likely shouldn't appear on CVs.

Seek other funding sources, e.g., the conference itself or a national funding body, perhaps ask your advisors for suggestions.

Whether you and co-authors pay yourselves depends on personal factors, e.g., can you afford to?

As the answer of user2768 has stated, doing research which leads to an accepted abstract at a conference is a good accomplishment for an undergraduate. Congratulations. Doubly so since -- for whatever combination of reasons -- you don't seem to have extensive support from your more senior advisor(s).

If you find the funds to attend the conference and present the paper, you will turn this into an accomplishment that will be meaningful on your CV for years to come, not only to be admitted to a Masters' degree but afterwards. You will also hopefully learn a lot at the conference and begin to make contacts, which is valuable in its own right.

However, I deviate from the other answer's perspective that if you need to withdraw instead, it shouldn't appear on your CV, and would indicate lack of foresight or disrespect. This may be true for an established academic, who has or may be expected to have a stable portfolio of funding, but is not true of an undergraduate or other emerging scholar. (I hope this is true in all fields.)

If you are unable to secure funding for at least one of your team to attend to present and do need to withdraw, I think you should definitely mention your accomplishment (marked as "accepted abstract at ___" and leave it at that) on your CV at this stage in your career, especially for the purposes of Graduate School admission. It will help document, as you said, that you do have research experience of some sort already. Were I on an admissions committee, I would look at it favorably in this context.

The difference comes afterwards. I suspect that when you are job hunting after your graduate degree, you will censor out such an "incomplete accomplishment" because you will have more recent, more standard, and "completed" conference presentations and/or publications. While if you do find the means to attend the conference and present, the presentation will remain a line item on your CV documenting your sucessful research activity is of longer duration. This will quite likely have incremental value at that time.

There will, of course, be purists who will argue that nothing should ever make it onto your CV that will later be censored out (i.e., that your CV is a universal and evergreen list of all your accomplishments, as opposed to a résumé, less used in academia, which presents a subset of accomplishments chosen as most relevant at that moment for a specific purpose.) That is, perhaps, a good overall aspiration. But there are many junior academics who have at various points listed "submitted" or "manuscript in progress" items on their then-current CVs, since those were meaningful accomplishments at the time. But where for various reasons those items did not progress further, and were silently removed from the CV later.

Admissions committees get it! And they want to see whatever evidence you've got of academic and research experience and potential. So congratulations and good luck!