How much do you think you can earn each month, multiply that times 3 to 12.
I'd want to know why it was dropped. Was/is the PR real? Was the domain age retained? How old was/is it? Any backlinks? How many, what kind, how spammy are they? Was the site de-listed? etc....
What kw's does the site focus on, and how profitable are they? What's the quality of the backlinks anchor text?
PR alone isn't going to deterimine it's value. On the other hand, a PR 7 site could be work quite a bit, depending on all the above.
I'd wonder how you acquired it, given that domainers make finding these opportunities a full-time occupation.