If you're doing long-range planning consider saving up your credit card points. Go as early as you can to acclimatize (the humidity is the tough part) and stay afterwards to enjoy vacation in full recovery mode. 2 weeks is perfect although I'd live there forever if I could. Especially cool is the Ho'ala IM training swim the Saturday 1 week before the race to shake off any jet lag.
Food is expensive so I'd suggest getting a condo/townhouse with full kitchen. And we prefer to stay away from the hubbub (we like Waikoloa Beach for the easy running and congestion-free riding) so a rental car is a must - plus the island is huge so to see anything you'd need this anyway.
Airfare from YVR: credit card points
Rental car: credit car points (I think I had to top up ~$200 CAD for my sub compact)
Townhouse: $120/night USD
Costco for major food purchases: ~$200USD including beer and wine. We don't eat meat so that saves a lot, and the fish - ahi tuna and ono in particular - are a relative bargain)
Costco for gas (only had to fill up twice in 2 weeks - and it's cheaper than in Vancouver)
IM Village: YMMV but there is some neat stuff so plan on buying yourself something
The race: can't remember exactly but it was something like $750USD?
Additional food/drink/shopping/gifts: $500USD seems about right depending on your spending habits and number of people traveling with you.
At the end of the day it's a really cool experience and totally worth it. And thanks to the points it was less expensive than the Ultra 520K for sure.
Kiwami NA Racing Team