Should I go to my friend's wedding?! After a plane ticket, hotel, tux, and gift, it'll cost me at least $600!

I'd call this friend NOW and ask--hey am I a groomsman or something? Why do I need a tux? He may say "doh I forgot to ask you" or "Oh that's right only A & B need tuxes, sorry!" We have a friend of my FH coming across the country on a month's notice to be with us. I don't care if he's in a t-shirt and jeans, just happy he's there! And our Groomsmen--we're letting them wear suits, and we bought the matching ties....Please, they're already paying their airfare!!