NEWS FLASH!!
After researching and researching, I nervously pushed the "book now" button on Hotwire for what I was 99% sure was the Westin Copley (Back Bay) Place and indeed it was, and I got it for $134 a night.

For end of July, that is quite a great deal! So excited! Still looking into a good day trip to the beach - thanks for all the great input so far!