CheckDog will do 100 pages of spell checking for free http://checkdog.com/.Don't know of any place that does grammar checking. I wonder if there are any mechanical turk third party providers that do that?
In my case, I run a forum with thousands of pages of user generated content. I can't afford the spell checking services for that amount of content, and I'm OK with leaving things in the user's original voice. What I did do was go into Google Analytics and export my top content by page title, 500 titles at a time. I copied and pasted the spreadsheet column with the titles into Word, and found the spelling errors in the titles of the posts. I went back and corrected those.
