Paul,
It's Gareths 40th birthday when we are over in August and I have booked flights for us (2 adults 1 child) with Blue Water Balloons. They charge $185 per adult (or $165 if booked over the internet) and $90 ($85 -internet) per child up to age 10. They also do a special flight offer for 4 people and they charge $640 for the 4 of you, again this may be an internet offer. I haven't had to pay a deposit (I have had to give them my card number though) and you only pay when you have flown. I think you can also cancel up to 48 hours before the specified flight day.

Hope this helps.

Gill [msnsmile]