And what to you mean by "build"? Are you literally starting from scratch? Walls, floor and ceiling? Or do you already have walls that just need to be treated? What furniture and props to you have available?
As Wheat said, you need to define "sexy." Or, better yet, how does your client define "sexy"?
And, of course, the big question... What is your budget?
Just saying "low budget" isn't much of a help. $100,000 for audio post can be considered low budget as it's less than 1% of what would be spent on a "Hollywood" budget film. However, for most indie filmmakers, $100k is still in the realm of fantasy for the entire project, much less just the audio post.
