It is free to sign up for a Sendle account.
By using this link to sign up, you will, in addition, receive a one-year free Premium business account (valued at $120) and save $1 on every parcel compared to their Easy account.
Here is an overview of Sendle Domestic Rates and Services.
If you would like to get in touch with their business team, you can do so here.
You can also find answers to most of your questions in their Help Centre.