Someone correct me if I'm confused, but to the best of my knowledge there isn't a "least expensive" garden view. There's garden view, lagoon, and MK view categories, and price for each room in the category is the same unless you consider concierge.
If you aren't staying concierge, you won't be in the Hawaii building. Otherwise with a garden view room you could be in any other longhouse. You may make a request, but there's really no way to know before you get there.