Titanium sprockets and chain are commonly used in bicycles. There's a few problems with that though. It's still expensive, the chain and sprockets are slightly narrower than #35 chain, so you aren't going to be able to bum replacements off someone at a competition.
Also, they come in very limited tooth counts. You'd also have to make an adapter to mount them to a shaft/wheel with, since they mount onto the cassette very differently than you would mount a sprocket to a shaft in FIRST.
Overall, really not worth the effort. Just use #25 chain and sprockets
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The chain alone is going to run you
$350 each, and you'll need 4 of them.
The cassette is
$150 each and you'd need 4 of them assuming you want to make a 4 WD robot.
And then you'd need to buy a set of chainrings, which are also going to cost you a pretty penny.
There's no easy or cheap way to do it