Serene responded:

There's no need to give excuses, especially ones that are easily seen
through. It's fine just to say, "Oh, sorry, we won't be able to make it
(or "we have other plans that night"). Have a wonderful time!"

But that *is* an easy-to-reveal excuse unless you plan to abandon your house
that evening simply to avoid being caught in a lie. Why not tell the REAL
truth? "I'd like to come to your party, but I think it would be too much of
a burden for me to provide two expensive bottles of wine and roasted beef
tenderloin for twenty people, most of whom are strangers to me."

Bob