Most of her books are out of print, but happily many are becoming available for e-readers. Although they are out my penny-pinching price range ($10), I was happy to see that one of her trilogies is available for less. Each book is $4: Vittoria Cottage, Music in the Hills, and Shoulder the Sky
Even better, those with Kindle Unlimited can read these for free.
Although these don't have "classic" Stevenson status, they would be a good introduction to her writing. I have not read the first two, but plan to give them to myself for Christmas.