I'd get the quotes. It wont cost you and you will have a reference for how much the price difference is. Also if you do go ahead and buy a split system from HN you will still need to get a licenced installer to put it in so factor that cost into the equation (not sure how much they charge in WA).

Can you zone/close your living space from the rest of the house so the system isn't working too hard to cool the house?

Also have you considered an evaporative cooler system? THey are good for dry climates (no idea what WA's climate is like in summer). It may be more cost effective although modern split systems can be pretty energy efficient if you get the right type.