Butler is really, really good. He had >8 offensive win shares last season by merit of his 21.3 PER on 21.6% usage, which makes him an excellent offensive player. Defensively, his reputation is deserved. That adds up to a really phenomenal player - not the best 2-way player in the game but quite possibly top 5 (LeBron, AD, CP3, Westbrook, Butler).
I think any GM in the league would offer him the max. The hypothetical 'double max' maybe not, but 1.5x the max? Quite possibly.