That depends on how you market your site, ads, paid memberships - and the list goes on and on. Even though you might have a PR5 site, a lot of income resides on you. I have seen very popular sites that have no banners on them and were totally supported by paid memberships. These sites seem to be of higher quality then free sites because the trolls to not last. What kind of site is it? What kind of services or sales do you offer? You say its a blog, ok?????? And that is it? No forum, no store front, no paid members sections?? Your question is VERY open ended and more information is really needed. See above.
The answer for this question is very relative, depend on your 1. Niche, 2. Geographic target, 3. Traffic (alexa) I have a PR6 site that alexa around 100.000 but didn't earn anything
If you've picked up dropped domain that still hold's its PR, then you can do what so many people on DP do - load it up with wordpress, write 10 posts and sell links on here to newbs who don't have enough experience to check what is in google's cache and take a look at archive.org. You'll make an easy buck, but won't have many friends.
Alexa ratings are over rated. To promote alexa is to promote spyware. The only hits that count towards your site are the people that have the alexa spybar installed. So as spyware removal tools get better, and more people use firefox, expect your "alexa" stats to go down even more. If you want real stats, use directly measured traffic tags - quantcast or google analytics. All spyware should die, and that means alexa spybar as well.
With a PR 5 blog you could sell links. Remember PR isn't always indicative of how much a site is worth.
You might be able to sell five or ten links for $20-100/year, depending on the buyer. Traffic is more important imo.