How much that person want to buy?? If he or she want to buy below $200 per year, don sell it.. Your price should be more than $200 per year because most of my PR4 site, I sold the link around $200 per year but in a related niche.
If different niche, sometimes the seller will pay more than that.. But, it depend on your site quality too.. If you site has a very high quality you can demand..