She does sound like a sweetheart, and she's very pretty, too. Personally I don't think the $1000 is that far off the mark...I know that many purebred breeds go for nearly that, plus she's been spayed and has all her shots. But I think that $1000 is a big chunk of change for most of us.
I suggest you look for internet sites for English Mastiffs to list her with - I know the Siberian sites usually have a "purebred dogs for sale" thread. Hard situation, I hope for her sake it has a happy ending, keep us informed? I hope your Grandfather gets to feeling better, too.