No, upvotes are NOT free.
(1) Each time we vote, we lose about 2 percent of our Steem Power, and that takes a couple of hours to get back. We can't vote more than about 10 to 12 times a day, or we risk losing so much power that the value goes down a lot. So we have to conserve our votes, and that's tough because there are so many good posts here on Steemit to vote on.
(2) We could just be selfish and vote on our own comments to earn the money from the vote. By voting on somebody else, we're giving up the money we could just give to ourselves. In that way, it is also not free.
Still, I understand that it's tough to gain attention when you're new and don't have a lot of followers or a strong upvote.
You're so nice for commenting on this post. For that, I gave you a vote!