It’s hard to say witout the website and more info. How often are the pages spidered (this is a more qualitive measure of PR, IMO)? How many pages? How many other links are there?
Basically, everything is worth what people will pay. If someone is selling a car, and the highest price someone will pay is $x, then the car is worth $x. So… how much are you willing to pay?
ALso of people say that getting too many links too quickly can get your a penalty on Google. You might want to check up on that and decide weather you are happy with that risk.