How much are links from the "muzzle"?

Recently, I am getting more and more offers to place links on my website www.prokoni.ru (about equestrian sports). I already have a regular advertiser who places a whole block. He was just the first and long-time wholesaler. Those who ask for accommodation about the placement of 1-3 links have already been refused for a long time. It is difficult to track payment, you need to update the links, and the money is small. However, I previously did not attach much importance to links, as a significant item of income from the site (the main thing for me is the placement of themed resource banners "from the industry": shops, etc.) Now my attitude to this is changing a little. Especially after one American advertiser began to “pay off” for one link the amount exceeding the cost of my server’s monthly collocation :)
That was the question. Rather a few:
- What is the cost of links from the muzzle of my site?
- how many such links can / should be placed without compromising the attractiveness for placing such links (too large number). what a limit.
Here I accidentally came across a resource that, according to a certain algorithm based on CY and PR (as I understood it), gives an estimate of the cost of the link. With prokoni.ru parameters, CY = 1100 PR = 3 (recently, it seemed like there were 4)
Those. block of 15 references at this price - $ 267.3
Well, some kind of discount is probably given for the amount :)

Can someone competent in this topic help me with any valuable information?