This is a situation that happened a couple of years ago and it still boggles my mind.
DH and I know another couple, let's call them S and B, who are fairly strapped for money but love to go out and party at any opportunity. (Probably the chance to talk to adults - they have 5 kids which is why they're strapped.)
S's parents gave them a pair of tickets to the symphony, which was for a special New Year's Eve concert including a formal party. Not exactly cheap, as you can imagine.
They invited us to come keep them company at this event. Did they offer to buy our tickets? No. Did they offer to split the cost of our tickets? No. OK, I could understand that they couldn't afford either of those options. Did they offer to at least feed us before the event? No. In fact, when we arrived to pick them up (yep, we were expected to do the driving too!) we found them being served dinner like royalty by S's parents, who were babysitting. Did they offer us anything? No.
Am I wrong to feel that these people were rude, or at the very least, presumptuous? It seems to me that if you're going to invite someone along to an expensive event, you either help defray the cost of their tickets or at least offer to treat them to a meal (which really doesn't have to be expensive at all). As it turned out, they got free tickets, a free dinner, and free transportation - while we had to pay for our tickets, get our own dinner, and provide the transportation.
Had it been entirely up to me, I would have turned down the invitation, but DH really wanted to go. He lets people like these walk all over him and calls ME the rude one if I protest.