I’m having a similar problem. I have a page with several dollar amounts, and it’s cutting the dollar sign and first two digits off when it pulls it into the “Notify Users of a Post” screen.
For example, “$123,456” becomes “3,456”.
I tried replacing the $ with the ASCII code and it worked long enough for me to save the post, go to the Notify page and send, but then TinyMCE threw the $ back in place of the ASCII codes (insert rant about TinyMCE).
Using the most recent versions of WordPress and Email Users. With this exception, your plugin has worked perfectly so far!