we developed our own solution easily on my new school website using the jquery contactable plugin coupled with unfuddle - a cheap and well-thought-out online bug tracking / project management. Posting through this interface adds a ticket to our debug tracker. Easy for us, and easy for the user, how he can comment while looking at the page. Through PHP, I used the browser detection function to pre-populate the user OS and browser form, as well as the URL of the page itself on which it is located during commenting.
It's about as cheap, but professional, as I could imagine.