Welcome to the Forum, Gailye :)
I find the best place to buy Richie's out-of-print books is Amazon.com.
^That link^ should bring you straight to a list of copies of The Scarecrow. Anytime you buy a used book from a seller on Amazon, it's going to be 3.99 for shipping. Other than that, the prices of the book it self can vary greatly. I see a copy there rated "Very Good" for just $1.98 (+shipping). Obviously it is up to you to decide which one you'll buy, but I hope this helps you.
You can also find most of her other books on Amazon as well. If there's still one you can't find, I suggest trying bn.com or ebay.com. The only problem with ebay is you REALLY have to watch the shipping prices, as some sellers can be quite expensive.
I really hope you find what you're looking for and hopefully you'll be back to talk about some of her other novels in the near future! :)