Salary
Average Salary: $54,000
Expected Lifetime Earnings: $2,254,392
The typical wage of a millwright is about $50,000 per year (source). Add in the bonuses you could get for working on the holidays, as well as overtime pay, and you could end up making closer to $76,000 per year (source). Maybe even more. It's up to you and your work ethic.
Your salary will also be somewhat dependent on where you decide to live. Starting your career in Houston can get you way more money, especially if you stick around and get a pay raise for tenure.
If you choose another location without the same plethora of industrial machines that Houston has, you could be looking at the other end of the spectrum—a salary of $35,000 per year (source). It's not terrible, but it'd be hard to afford groceries at the farmer's market on a salary like that.
The final factor that'll determine your salary is your ability to chase down jobs. Most millwrights are guns for hire. Well, they're actually mechanics for hire...though, when your job involves all that heavy lifting, you're likely to have guns as well.
You'll most likely work contract jobs, which means that you'll spend a couple days or weeks on a single project and then have some downtime while you hunt for another gig. It's a little unpredictable at times, but you can still make a decent living, especially considering this career only requires a high school education.
Add in the fact that many millwrights get medical, dental, and vision insurance coverage (source), and you can see why somebody would want to go into this career.