Are both sentences grammatically correct? He owned an industry with revenues of $20 million to $30 million a year. (Certainly better than: a $20 million- to $30 million-a-year industry, right?) He owned an industry with annual revenues of $20 million to $30 million. (Adding the words "a year" at the end of this sentence would be redundant, correct? And should the word "between" precede "$20 million to $30 million" in each sentence?) Thank you.
I think they're both correct. But "industry" sounds wrong to me. Industry usually refers to all companies in a specific area, as in "the steel industry".
Is this fiction or non-fiction? And did he own a company or an entire industry? If you're making a point about monopoly, I'd add "entire" for emphasis. In fact, I'd probably just say: "He owned an entire industry, with revenues averaging 20-30 million dollars per year."