Ren-Faire is performers and a paying audience.

SCA is just strange people having fun.

Ren-faire is a concept used as the basis for several unrelated for-profit companies, SCA is a particular world-wide non-profit organization.

I understand the Aussie SCA kingdom (Lochac, which includes NZ and Antarctica) is remarkably intense. The web site: http://lochac.sca.org/lochac/
If they are anything like the USA version, they are very welcoming, but may ask you why you are naked, modern clothing being ignored. They may have clothing for you to borrow. They will include you and make sure that you have fun. Unlike ren-faire, you will spend little or no money.