Well, judging by the economics, a couple of era-millions. I am saying era millions simply because inflation happened. I can talk to you with numbers. What cost $1,000,000 in 1800 would cost $13,708,645 in 2014. So, in term, if a city wanted to take a World Fair, they had to have some millions, but if you take those millions and convert them to today's dollars, the number would be much bigger.

TL:DR: You cannot say, simply because inflation has happened over the years.