Is this possible to expose a report via the high volume portal?
Are there any visuaforce/apex examples of how to do this?
Only certain objects can be directly exposed using the HVCP license. Accounts, Contacts, Opportunities and a number of other Objects are not directly supported by that license. What you have to do to work around it to use custom objects and triggers to "mirror" them through a custom object that portal users can access and view. In essence, you duplicate everything as a custom object that portal users can then see.
I suggest you take a look at Communities and build a portal around that model if you want to pursue it. That's what I've been working on for the last several months. Fortunately, we're close to finishing and heading towards our final testing phase.