In order to work with our service, any file-hosting service must be able to provide a static URL (a URL which does not ever change) to access each file directly, without requiring the downloader to go through a "download page" nor even use an actual Web browser program (since it will be our back-end download scripts accessing your remote file, not the buyer's browser directly). You would also need to be able to set your files as publicly accessible or otherwise obtain a public URL to access each of them, without needing to log in anywhere first for authorization to access the files.
BTW, we mean "public" only in the sense that they can be accessed without restriction if the exact URL to each file is known, although those URLs are never exposed anywhere for the public to discover, and E-junkie buyers would never know nor access your remote file URLs directly. It's rather like having an unlisted phone number; anyone who already knows your number can call you, but nobody else has any way of finding your number, or even knowing that you have a phone at all, if you don't tell them -- in this analogy, you would be giving your number only to us, and we don't share it with anybody else.
Another affordable file-storage option we recommend is Amazon S3, which may even be free depending on your usage stats there, and extremely inexpensive otherwise:
Their terminology can be a bit confusing at first (they refer to files as "objects", folders as "buckets"), but it's really pretty simple to set up; here's their quick Getting Started tutorial: