Black tie wedding guest dress?

Hi!

I’m going to my very first black tie wedding. It’s in Nantucket in the summer and I’m at a complete loss on what to wear! I’m midsize and typically wear black. I do love wearing color too but black is just what a gravitate toward (I’m pale and get washed out easily lol).

So, I have two questions -

1.) What brands are best for black tie wedding guest dresses? Budget max is $300.

2.) What materials do you think are best for humid weddings (it will be outside)?