Like this study that looked at the summer and winter Olympics from 1960 through 2014 and found that the summer Olympic Games went over budget by an average of 252% - which means you ADD 2 and a half times the budget cost, so a hypothetical $3B games would actually come in at about $10.5B(!)
As they call out in the article "Unfortunately, Olympics officials and hosts often misinform about the costs and cost overruns of the Games."
This analysis was done based on the estimates as of the time of the bid country being accepted. And on the actual games-related costs excluding infrastructure. As you might guess, in the years after the bid the budgets get adjusted many times so that the project can be 'shown' to come in close to budget. London was a prime example (in case anyone thought that came in anywhere near budget).
Let's go Rio! (As in, let's keep up this trend so it's less likely we'll ever bid on them again)
