You can't afford it and you don't wanna so don't feel guilty! I wouldn't be able to cough up $3000 either! That's why it's an *invitation,* not an order. You are allowed to decline.
Going to weddings brings up all kinds of bad/sad feelings for me so I've declared a moratorium on attending any weddings for the next 4 years (last one I went to was over a year ago.) This means if I get invited to a wedding I will decline for my own sanity, cost etc doesn't even factor into it.