This is an interesting line in itself. If you look at it closely, it's saying that a book is the best "Frigate" there is. Does that mean that it's even better than a real ship?
Nor any Coursers like a Page Of prancing Poetry (lines 3-4)
Like in line 1, we wonder if the speaker is suggesting here that reading is <em>better</em> than actually traveling.
How frugal is the Chariot That bears the Human soul. (lines 7-8)
There's no exclamation point here, but there totally should be! The speaker is amazed by how reading – which costs nothing – can transport us anywhere in spirit. Here, we see her amazement at the power of the human imagination.