Most caterers already have an idea of what it costs to get to the event, pay a helper or three,
pro-rate for insurances, etc. The remaining costs are event specific,(food, supplies, rentals, chaffer-fuel etc)
I just thumbnail it out per person.
Now, when you say "make a profit" that's a subjective thing-- and to me, size matters--e.g., on an event buffet of
say, 250ppl or so and under I find it's not hard to make 30 to 40% net, while still staying price competitive.
While on big parties I've settled for less % because in the end you make more actual. . . .dollars.
However I must admit that as yet, that figure has not nearly approached the MILLION posed in your question.