Question: For faculty lack of funding, how to find conferences that allow people to sit in without paying? For those that don't allow officially, will they check attendees' badge?

Answer: 
It depends on the conference. In recent years, the College Art Association, an annual conference for art historians and artists, has instituted a ["Pay-What-You-Wish"](https://www.collegeart.org/news/2019/02/05/pay-as-you-wish-is-back-for-caa-2019/) option. This was instituted after many adjuncts, students, and others expressed their inability to pay fees to attend an integral conference in their field. I mention this in case you are a member of an organization that holds conferences. As a member, you may be able to make your voice heard through elections and other ways that can foster a greater awareness of the high costs of attending conferences for underfunded faculty members. Hope this helps.
Conferences might give a discount for people from developing countries, for students, and for people who are early in their career. Otherwise discounts are not given. Even attendees who are invited to receive a cash award usually do not get free admission.