SSL on WordPress: Cheap v/s Expensive SSL certificates

I'm exploring several SSL certificates for my website. My primary requirement is to secure the wp-admin directory and also certain pages of the front-end where we collect some basic info (name, email, phone number) from our users. We don't collect and don't plan to collect any highly sensitive information such as credit card and bank account details.

I have found several SSL certificates and their pricing ranges from $4.99/yr to some priced as high as $1000/yr.

My question is how are these certificates different in terms actually securing the site? Value of assurance and different type of validations aside, are there any technical benefits in terms of security with the more expensive certificates?

Additionally, is there a good way to actually implement SSL on a non-multisite WordPress site without any significant hassles?