I want to put in another nod to the charity tournaments held at some of the courses which might otherwise be inaccessible to outside/non-member play.
There is no denying that there are sometimes considerable costs involved in such events, but these are often wonderful charities who depend on these events for much of their fundraising/public awareness during the year.
Either I or close friends have played the following courses during the past 24 months in just such a fashion: Winged Foot, Sahalee, Shoreacres, Plainfield, The Creek, Piping Rock, Myopia Hunt, Olympic-Lake and Oakmont. Another alternatives might be GCA-sponsored outings, which have taken place at similarly top-notch clubs such as Baltusrol and Hidden Creek, to name a few.
For some with lots of disposable income, the costs of these rounds might be similar to that year's new driver, putter and fairway wood combined. For others, it might require more savings and personal sacrifice, or travel from a remote location, such as the Pacific Northwest.
It all depends on how much one wants, or to what lengths one will go, to indulge one's hobby/passion/obsession.
As with many things in life, it is always possible that some doors may be opened for you, but other doors might need some more active participation to be opened.
I can only comment on personal experience, but here is one example. There is a Special Olympics event at Myopia Hunt Club each October, at a very reasonable price for a charitable function. Sure it may be on a weekday, and the weather might be marginal on a given date, but it is a terrific opportunity to support a wonderful cause, and have access to a club that most of us would never dream to be able to visit. The event has not filled either of the last two years. Every student of GCA thus has the oppportunity to study this course first-hand, not through readings or someone else's photos.
Do you want to visit a course only on the weekend, or at an inexpensive guest fee? Such charity events are not for you. I would hazard to say that all but a handful of clubs in the US are indeed accessible to anyone who wishes to put their money where their mouth or heart is. The club itself is typically quite helpful in letting one know if or when these events will be...