Just thinking -
Don't know how big or how lavish this party will be -
But -
Say you are paying $1000 for food and beverages - but have no travel expenses
And they are paying $1000 for travel to be there - but are paying for none of the party expense -
And this is all for the benefit of the parents celebrating their 70th - - - -
???
Don't know what everyone's financial condition is - but assuming that you are all more or less equal -