I guess that would depend on the value of the gift card, and whether you are buying it via an auction, or redeeming points. Here's a sample of one gift card and options:
If you find one in a daily deal it would be for $5-$10 and it would be between 500-1000 points. You would have have to pay anything. For the $25 gift cards you would have to win it in an auctions and that will depend on how many points you bid.