Great question! All of the upgradable files on Vecteezy cost 1 credit.
If you don't have any download credits, you can still download and use the files on Vecteezy; you'll just need to review the "license info" on the download page. This page will tell you how to give attribution to us for the file.
If you don't want to give attribution on the files you download, you can purchase credits here. Once you purchase credits, you'll start to be prompted to make a selection on whether or not you want to use your credits when you download a free file. Using a credit gives you broad commercial rights WITHOUT having to give attribution for using the file. If you don't want to use a credit, you'd select no, and provide attribution back on that file.
There will be some files that do not allow for you to use a credit, meaning, they don't allow for commercial use without attribution.
In any case, you may not redistribute the file itself.