Of course, the subscription is $25 per year; but that's only for the iTunes Match functionality
. You get zero additional storage space for the subscription price.
The way iTunes Match works, if Apple has a song from your library in their catalogue, they do not count it against your iCloud storage space limit. If, however, iTunes Match needs to upload a song from your computer or device to their server, then the space needed to store that song on their server is taken away from your iCloud storage.
The situation gets more complicated in that iTunes Match is pretty buggy in recognizing even legendary songs and albums, which they definitely already have on their own server. But, because of the bugs, they will needlessly upload the songs from you to them anyway, and correspondingly decrease your free iCloud storage amount.
Further, I'm perplexed as to how you only have 1 GB of cloud storage.
Do you mean 1 GB free or 1 GB overall? I thought every holder of an Apple device is given 5 GB of free iCloud storage space. I then bought 10 GB more for 15 GB total in my iCloud account.
If you find that iTunes Match works for you now
, it may not work for you later on. Your free storage space may get exhausted over time, in the way described above. Also, if you have a huge music library and have only just subscribed to iTunes Match, the matching process may still currently be ongoing as we speak. People have reported it may take an entire day or two for iTunes Match to successfully scan a user's music library if it's very large.
Hope this helps, even if it's not directly related to e-books.