I'll say

final say

The right to make a final decision.

have a say

To (receive the opportunity to) voice one's opinion.

I'd say

It is my estimate or opinion.

I'll be

Expressing surprise.

I'll be a monkey's uncle

Often preceded by well: expressing complete surprise or disbelief.

I'll be bound

An expression of surprise.

I'll be damned

An expression of surprise.

I'll be danged

An expression of surprise.