There's no cost, it's free during testing (I'm covering the model fees). There's usage caps per key, with current usage indicated to each user when they are logged in. Auth is NIP-98, and you sign a kind-27235 challenge to log in. The terms acceptance itself is a kind-1 that you sign whose content is the full Terms text, which gets sent to me for my records. The signature is necessary partly because your input is forwarded to the model provider and I have to consider their own terms. If you'd like to try it, you can sign the Terms under Settings > Inkan Settings > Service Access and let me know, and I'll switch your key on.