What is the best website or way to buy airfare last minute? Hotwire and what else? Best airfare to brazil?

There is no best website to buy a last minute ticket. They will all be pretty expensive. You can consider http://www.priceline.com/ and use the Name Your Price feature. However you must make sure you read and understand the fine print and conditions. Supposedly you cannot cancel or change the ticket once you agree to purchase it. Therefore if you do not make the trip, you are still out of all the money you paid. No travel voucher will be given. Also you may have really long connection times or inconvenient flight times.

Hotwire is one option. Other options can be Expedia, Travelocity, Priceline. It is also worth going to each airline site one by one as they do offers specials sometimes which are not available on any other internet site

Cheapest Airline Biz provides some good information.