Becoming a member on Secret Builders is free! you are able to buy many cool items and do many cool things, but there is an option to become a paying member.
See the photo above for details, you can view this properly on secret builders here https://www.secretbuilders.com/Payment/subscribe.jsp
its really cool and worth looking into.
If you dont become a paying member you can still play quests and earn silver shills but you will not have all the benefits a Super Builder member would have.