Deploying the Rule Engine in a Rails Application

I want to implement the Rule Engine in my Rails 3.2 application, which has a complex pricing logic, I want to convert the conditions in the pricing logic into rules and use them. I am creating a completely new application for this purpose.

In this regard, I searched a lot on googled and found rules_engine, ruleby, treetop, but the documentation that they provided was not only sufficient, I struggled a lot with choosing the best one suitable for my requirement.

What is the best approach to start development on the rule engine?