Idk how much storage it uses, probably a few gigabytes, although you can easily get *huge* drives these days. I've seen 20 terabytes for under $300 USD even on Amazon, and I'd imagine there is a way to get ones cheaper than that for similar sizes. I've seen like 14 or 16TB for $200~ now as well. To add more storage, if the site is self-hosted, just buy another hard-drive and hook it up. Shouldn't be too hard, especially if it is on a proper server-rack and not an old laptop or desktop. If the sites are run on a VPS, then you'd likely have to talk that out with the VPS provider.