If the link is in an article that can drive genuine, quality traffic to my site by people who will be interested in learning more about my servers / products, I would pay up to $300 (depending on the site).
If someone approached me to ask me for a link, which is not spammy but relevant, I would ask for about $150.
it depends on your customer base and product . SEO mainly for branding, and indirecting lead to online sales if your product allow transact online
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