It all depends on site owners. Some charge higher if their pr is high. Try to negotiate prices and get the maximum from the deal. Don't try for the 100 links at once. A few quality links from higher pr sites would be better.
100 backlinks is nothing, no one selling that amounts here ((, Bu I think if you want to purchase for example 100 directory backlinks the cost on the market is aprox 30-60USD, but that is a wasting of money. Forum links are much cheaper.
Check out for paid listings on google. There are many out there which offer backlinks for $10 or less.
I agree that this is a really big range. I've seen offers for 1500 links for $300 and 1 link for $300. Quality (PR) of the link will always raise the price. In the end, you usually can expect to get what you pay for. Whatever method you choose for getting links and however much you pay, a link is near worthless unless it is from a relevant site/directory/blog or a high authority site.
Hello I already have huge collection of all kinds directories, articles sites, high PR forums My client site is already boost in PR to No 3 Thanks
I am using GAF and pay about 10 cents per, so your total is going to be 10$ per 100 backlinks. If you want links from pages with PR3 and higher price will be about 300$ But if you need links from GOOD sites that has good PR and related to your site. Price will be about 10$ per link. Total 1000$.