You can store up to 5GB of data for free on your iCloud Drive. This includes all of your files, not just Astro Gold. You may need to pay for extra storage. However please note that each Astro Gold chart takes up only about 200 bytes of stores, even a chart file with 1000 charts would only take about 0.2MB of storage. Hence in practical terms any extra storage space requirement is more likely to be prompted by your other file types.