I don’t think lurking around campus is going to lead to the same results as being immersed in a research environment full-time (especially if you’re not doing research yourself). I generally think that a large amount of useful knowledge is tacit and that it’s hard to absorb without being pretty directly involved.
Also as others have noted, a PhD is free / paid for so (economic) cost isn’t that much of a consideration.
I don’t think lurking around campus is going to lead to the same results as being immersed in a research environment full-time (especially if you’re not doing research yourself). I generally think that a large amount of useful knowledge is tacit and that it’s hard to absorb without being pretty directly involved.
Also as others have noted, a PhD is free / paid for so (economic) cost isn’t that much of a consideration.