Snapdocs is completely free to use for notary signing agents. If you haven't already, you can create your free Snapdocs account here.
All the tools and features available to you in your Snapdocs account are free. Snapdocs also doesn't take a portion of the money that you earn from signings. The fee that you see listed on a signing offer is what the signing service or title company is willing to pay you to complete the signing.