GP said 'open bar with 2 bartenders'. I.e. commercially priced drinks, and staff. Did you have those? If so, pro tip, next time just get a few cases of various drinks, plonk them on a table with a bunch of glasses (rented, if need be) and call it good. People can't drink soft drink for more than, say, 3 USD worth in an afternoon; and even if you served 12 years Glenfiddich to everyone including the children, enough of it to knock them all out, you still wouldn't have spend more than $1000.

So yeah still wondering what sort of party you threw. I mean, yeah it's easily possible to spend that much, but it's also possible to do it for much less and you don't even need to really try.