Start with your local library and any other libraries in your area, because they should be free to sign up for.
Then there are some that have an annual fee for out of state residents, this article covers many of them. I’ve heard that you can get around this fee at some libraries by picking a random in state address, though I’ve never tried it myself.
Additionally, the Seattle public library allows a free card for anyone in the US under the age of 26, and Brooklyn public library does the same for anyone under 21.
Great explanation, although I want to clarify that not all nebulae are galaxies. Nebulas are massive clouds of dust and gas that are found within galaxies. Other galaxies were previously thought to be nebulas in space outside of the Milky Way, called extragalactic nebulae. However, in the early 1900s it was proven that these were actually other galaxies and not nebulas, so the term is no longer used.
While there are nebulae in other galaxies, they are not easily visible to us, so the word nebula generally refers to those contained within the Milky Way.