Geoff,
Your welcome. I'm a huge shopper for deals and I love making my photography $$$ go as far as possible, so I enjoy helping others find the best deals too.
On Adorama's website, they say free shipping to Hawaii is excluded.
However, since you are looking at possibly buying multiple units, I would give them a call or PM Helen Oyster, who is a Adorama Customer Ambassador that frequents this forum. Perhaps they can provide you with free shipping. One warning though, Adorama is essentially closed until April 3rd due to their religious holiday schedule. But personally, unless you need the flash units right now, their prices and VIP Warranty are worth the wait.
Another note, and this may not apply...but over the last 7 months or so, anytime I purchase a higher-end item with free shipping, such as an 85L or a 24L, Adorama has shipped it (free) via UPS Ground instead of "Mail Innovations" or some other method that takes a really long time, which is often the case with free shipping. Smaller items, or orders only worth a hundred dollars or so have still been sent to me via the slow track. But higher end items have been arriving within 3 days via UPS Ground.
Hope this helps,
Bryan