If you were to purchase a blog ...
 

that was a PR4 with 10-15k+ a day. I have been told everything from $500 to $5000. Opinions please?

traffic doesnt mean much if it only makes 10 usd/day..

basically you need to give more info for an accurate evaluation.

Correct, unless you can see that traffic related to income of some sort to give you an idea of scale, I'd say bid very low.

around $500 a week income from it roughly