Hmm. I'm in two wedding this year and I've spent $600-800 on my plane tickets, renting a car, and hotel for the extended weekends. Both brides are doing their bachelorette parties the Thursday before the wedding, saving me another weekend trip.
One bride paid for the dress, the other didn't. I've spent $150 each on shoes.
One bride is paying for hair and makeup, the other isn't.
I'm not sure what the bachelorette activities will cost me, or how much I'll spend to eat during the times we aren't together during the weekend, but I'll probably come close to spending $1200-$1500 on each wedding.
I estimated those costs before I said yes. I wouldn't spend the money unless I truly wanted to be there.
Distant relatives and half friends only get a yes from me if they pay for everything, I don't have to travel, and I like the dress.