I have a fairly new website www.realestatewhangarei.co.nz that I am considering selling links on - currently it has a PR of 2 & 1 depending on what page you are on and gets around 1000 uniques per month. What would someone charge on a monthly basis for a link on one of these pages?? One dollar per month?
The link will be worth more than one dollar a month to find out exactly how much it's worth you should have your site appraised, you should go to google and do a search for website appraisal.
Are there many sites catering to real estate in the Whangarei area ? If not, you could charge a slight premium over the regular rate. For links, the rate depends on various factors. PR, traffic ( quality of traffic- area, bounce rate etc), age of domain etc.
Anywhere from $1/month to $10/month it depends how much your buyers are willing to pay for it If they want their PageRank increased they won't pay much for a PR2 but if they want to improve their SERPs they will pay more usually the price can go up if there is a lot of competition in your sub-niche (lets say "real estate new Zealand")