If it is only a few files, you can try to download under the Free User button. However you will need a lot of patience to do it. The trick is to clear the memory after a few unsuccessful tries and to do it during off-peak periods i.e. weekdays and non-peak hours. If you manage to download in a session, then you should keep doing because it means there is spare capacity at that time.
Payment by credit card for downloading as a Premium User is quite safe. They now have a new scheme which I don't know how it operates but it is good if you have a lot of files to download. Just pay for as low as possible first and if it is not enough, then subscribe for more.