It's important to note that the lady is not "trying" to buy a stairway to heaven, rather, she does buy it.
Why else would the song say, "when she gets there she knows if the stores are all closed, with a word she can get what she came for?
You are thinking and engaged in the composition and possible meanings.
For example, the word 'Book of love' on the song 'Rock n Roll', or the last song of the album 'When levee Breaks'. This thread is full of people with different backgrounds and mindsets.
Because there were same words on the song 'American Pie', too. One thing you have in common, in greater or lesser degree, is a degree of interest.
The first time I heard it, I was thought it pretty cool, but didn't understand it.
It sounded as if a lady who had money wanted to buy her way into heaven -- with that said, that's about all I understood of the song that seemed rather dark at the seams, with it's mystical, ambiguous language, all the while speaking about "heaven".
Surprisingly, the comments do not address some metaphorical or metaphysical aspects, and do not consider important cultural movements that were contemporaneous during the time of the initial creation and release of Stairway to Heaven.