There are many SSL certificate providers on the market. All these providers are authorized and may offer different prices. The price ranges between $49-$199 / year depending on the services offered by the SSL company.
Some of the popular SSL certificate providers also offer addons and services like installation of the SSL certificate on your website. These services come with additional costs for the user.
For instance, SSL certificate from GoDaddy start from $2.49 / month which is the best deal for a single site. They also help install the SSL certificate on your domain.