It does not cost you any money, but it will decrease you voting power.

You can give 10 votes at 100% before your power is depleted. It takes about 24 hours to regain 20% of your voting power.

When you upvote you might see a vote slider like this

If you decrease the percentage then you can stretch out your votes, meaning you can give smaller votes to more people.

You can see your total voting power at the following link: https://steemnow.com/@kwalker