I know exactly what you're going through. I ended up paying over 50 bucks of the cost of a "no host" luncheon for a departing co-worker (I grabbed the flowers on the way). Although I was assured I would be paid back, only half the people attending made any effort even after repeated e-mails. This was also for someone well liked, and the same rules applied as in your office. So I decided not to organize any more parties until I was good and ready. It didn't take long for everyone to notice, and so far, I've noticed that no one else steps up anymore either. The only thing you can do is to offer to take the brithday person out yourself, or ask the usual birthday coordinator if we're "doing anything for Cyndi this year?"
I would ask the other attendees what happened. If they offer to make it right that's great. If not? Cross them off your invite list.
If you did something to offend them, as previously suggested, it was up to the offended parties to make their feelings know, rather than just dump this on you. What if you were paying cash and couldn't cover the entire bill for the Honoree?