OK, but have you done your research for backlinks etc? Does it risk a ban? Is the PR real (this I would think so, because it's only 3, but u never know...) And obviously it depends how it got that PR, what sort of links and if it would be useful to you... With these funny updates a PR 3 can be so ridiculously easy with new websites that I guess I would definetely pay 20$, but maybe just not.
Just because it has some sites linking to it doesn't mean it's getting visits. Can you check the traffic before you buy?
i sold my PR3 in $25 so i think maximum you can get is $30 not more than that unless someone is in really need of domain or some newbie webmasters buy it. Thanx