I'd cut down on the cost of these parties so that if someone cancels, it's not a big deal. Why not have a group of boys over for cake and video games? Or for a sleepover birthday party? Or go to the movies? Or a BBQ and swim party? Why does it need to be so elaborate?
One thing I found was that throwing a party at home cost more money and takes WAY more energy than doing it anywhere else.
You've got that right! My son had his 10th birthday party this week and wanted a party at home as opposed to some other place. What to do with a dozen 10 year old boys and misc other ages (mainly girls)? Musical chairs and pin the tail on the donkey just wouldn't cut it anymore, so we too ended up booking a mad scientist party. Fortunately in our case the kids all had a great time and I'd recommend the science lady to anyone. It was $15/head, minimum 15 kids, but it was worth it as it took up 2 hours of party time so that all that was left was food and cake time. But I still had to clean the house, organise the food and keep everything under control. My younger son (6) had a party recently too. I tried to talk him into a bowling party but he insisted on having a treasure hunt party at home. With 12 kids by the time I'd divided per head the cost of food, prizes, balloons, partyware treasure, a pinata and take home bags it probably would have been $20/child, at least. Next year he is having a bowling party, end of discussion (approx $12/head all inclusive). Older son can 1 or 2 friends for a sleepover and that will be it.
I guess what I am trying to say is, it is often a lot more expensive to have a party at home as opposed to a location and you've still got to factor in cleaning the house before and afterwards. I don't begrudge my kids' their parties at all but I find it very offensive when someone cancels literally right at the last minute or just fails to turns up at all (barring something very serious like accident or illness). I have noticed this year that that has happened at every single party we've been to (and held), so it would seem like it was becoming more than norm unfortunately.