I can provide a quality of work in integration of Braintree Payment gateway with ruby on rails with all options like payment store, plans, recurring plans etc with mail delivery system. Braintree is subsidiary of paypal which is easy to maintain and more secure and have more payment options . This is my basic rate for integrating payment gateway. If you want full project, the price will be extended according to the complexity of work.
What the Seller needs to start the work
you should need a proper contact method like email,phone, INTERNET voip account like skype for contact . For code exchange you should need a private repository like Github, Bitbucket for the code , it should be because the code should not be shared or viewed by the public.