Don't get into too much bullshit dude, you are not selling an Audi or an Island. 99% of the times the value of PR links are what someone is paying, and what someone is willing to sell at.
You can find PR5 links for $15-$20 a month, or $50-$80 for permanent .. but at the same time you will find some sellers selling at no less than $100 a month.
Like Jdoughs said there are quite a few factors, but he just went into too much detail. May be his opinion was biased because he sells PR links himself. No offense meant Jdoughs.
Based on your details, here is the rough idea of what you can charge.
PR3 - $10-$15 a month
PR4 - $15-$20 a month
PR5 - $25-$30 a month
.. provided that you have no more than 15-20 outgoing links.
To get even better idea, browse
buy & sell section of this forum and see what other people are charging and what other people are willing to pay.
A quick tip, before starting selling them make sure you have some content on the site. Easiest way is to setup some RSS based automatic blog, with decent template .. so that your site doesn't look crap.