[kach22i]

Special elevating devices also known as residential lifts are an affordable way to go.

They are lower cost than elevators which cover more than one level at a time.

I'd opt for the upper garage flat.

I'm pretty sure that in Portland the resident of the "in-law" apartment does not have to be related to you, so there is some resale or investment value there.

You should be able to get a better design and an idea of cost from a local architect.

Try a small office or a guy working out of his house with low overhead to get the best price.