1. The airline probably won't let you fly when you show up with a kid covered in chicken pox. I suggest finding some family or friends who can help you with the money to do what you need to do in the meantime. See your embassy as a last resort.
2. It is completely wrong to even consider exposing a plane full of people to your child's contagious disease. While chicken pox is often a mild condition, it can be very severe and have long term effects, especially in the very young and very old. Why do you think they developed a vaccine? It is highly contagious, so there is a good chance that someone will be exposed and infected. Even if you could get away with flying with him, you shouldn't. It's just not the right thing to do.
I also found this:
"If you or your child have chickenpox, you may not be allowed to fly until six days after the last spot has appeared.
You and your child should be safe to fly once you're past the infectious stage and all of the blisters have crusted over. However, it's best to check the policy of your airline first. Inform the airline as soon as chickenpox is diagnosed.
It is also important to let your travel insurer know if you or your child has chickenpox. You need to make sure that you'll be covered if you have to delay or cancel your holiday, or if you need to extend your stay until your child is well enough to fly home."
http://www.nhs.uk/Conditions/Chickenpox/Pages/Prevention.aspx