I would say subtract your travel expenses and then add the food cost of other side parties that you are invited to. Divide it by 2 and a little more at your own discretion. Add or subtract $100 and round it up to the nearest dollar.
My suggestion is 300 to 350. It'll cover your plate cost and then some. But this also depends on how good of friends you are. You could get away with maybe 250 since you're alone but if you're really close that might seem insulting. At the end of the day you give what you can. Dont go outside of your means just because a friend decided to have an expensive or elaborate wedding. You're there to support the marriage, not to fund their lives.
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