Payment Page for Rails App

I need to create a page where a user c开发者_JS百科an go in. List the price of an item, the offer price for that item, and then add those two numbers and take a percentage of 15 then take that number and add it to the first two. In Math terms I mean Item Price(5) + Offer(5) + (Item + Offer)*.15 = Total and then from there I will have a checkout page where it will lead them to paypal to make the payment for the total. I think I have an understanding about the paypal part of it but I need help creating a page like that, I am still kinda new at this so I'm sorry if this question seems to simple.

Just one example:

A Ruby library for dealing with credit cards and payment processors: http://www.activemerchant.org/ (Github sources of the Rails plugin: https://github.com/Shopify/active_merchant - active development, last modified only 5 days ago)

A (recent) blog entry that shows how to use it: http://dev.otrobloggeek.com/2011/01/30/paypal-on-rails.html

Another option is to use the Ruby code supplied by Paypal in their developer section.

However, it seems you want much more step-by-step guidance for a Ruby/Rails beginner, but I don't think doing the work for you is not what this site is about, so, sorry, I only have those pointers. The linked blog does have concrete code though! Hope it helps!