> GP said 'open bar with 2 bartenders'. I.e. commercially priced drinks, and staff.

GP here, and no, that doesn't mean that.

It means you hire 2 bartenders to make the drinks, and you buy the supplies they use.

And, no, if you want a cocktail party, you don't "plonk a few cases of drinks on the table". That's also a fun party, but a different kind.