There’s no set amount for how much you should pay for backlinks, as this is very dependant on the type of link you buy, the quantity and quality of the backlink.
For high authority backlinks, this will naturally cost more that low authority, but it’s always a good idea to do your research on link providers before ordering outbound links.
Backlink buying can be a tricky business, but when done properly, is one of the best ways to increase your monthly traffic.