If he works with his hands a lot or isn't used to jewelry silicone rings are fairly low priced and come in a rainbow of colors.
I'm getting an engagement ring for my SO and it's a Benchmark brand of a ring, from their "FORGE" collection. It's a heavier metal they call tantalum that is dull and plain but exactly what he wants. This is the one I bought and it really is kind of unique and definitely durable. I went in to a store though to look at them in person and the finish looks a lot nicer than the pictures on the website. But it takes about 4 weeks to get and I ordered it 3 weeks ago, so I haven't gotten it yet.