Sure. Nothing is deducted from your wallet at all; posting rewards are paid through dilution, and the blockchain does not charge transaction fees.

The formulas for determining how much an upvote increases the post valuation are quite complex, and only reading the code will tell you exactly what they are, but the Steem Power of the voter is the biggest factor. Other things come into play as well, including how much stake has already upvoted the post, how much voting power the voter has left (the more you vote, the less each vote is worth), and probably others I'm not thinking of just now.