How about native Rhododendrons and Azaleas? I think drought tolerant shrubs is probably the way to go there, for easy care.
The Pacific Rhododendron R. macrophyllum is drought tolerant and several could go by the house.
Western Azalea R. occidentale is deciduous, probably wants a bit more water- if I recall correctly on the other side of those big trees is a stream so maybe plant some by the trees.
Then just let them grow, maybe a few Salal. You would need to water the first couple of years, then they should be fine on their own.
It is too late for this year, but the Rhody can be gotten from the annual Snohomish Conservation District plant sale at the shocking price of three for $8. Now that is cheap. Possibly there is some King County organization selling natives real cheap. Check out the Conservation District website, the plant list is still available to look at, it's the cheapest way to get plants that I know.
Other ideas. If you want to come here some day and dig I have some shade plants that could use a home- I took out a huge pine tree that I had plantings under. I have a yellow flowering epimedium that does not need any water at all (except the first year) and slowly spreads as a groundcover. Be warned you might need an ax or a saw to dig it up, but you could have lots. I have Alstroemeria ' The Third Harmonic' which settled into that dry shade and has spread a bit, and I have 'Yellow Friendship' too but don't know how it does in shade. They could end up invasive, but in a dry spot seem ok. There are other plants I specifically placed there to do well in dry shade so I would not need to water much.
