Custom shopping cart for existing web app & financial system integration

General information for the website: Selling digital goods (selling classified ads on line)
Kind of development: Customization of existing website
Description of requirements/features: Looking for a developer for custom shopping cart, that will become integrated with part of existing web application. The application is written in ASP.net and VB. net 4.5 and SQL Server 2014.
You must have experience successfully integrating with one of financial processing system like PayPal or Stripe or other.
The shopping cart will accept the information about the products selected. Then it will sum the purchases and generate ShoppingCart_ID number (I have the code for this part). Once the customer is ready to finalize the purchase, the shopping cart will perform update to one or two product tables pending the product in the shopping cart. Also the shopping cart will transfer all needed data (total, CustomerID, Customer Name, email address, product id, ShoppingCart_ID, ...,.... to the financial processing system.
Once the purchase is completed, there needs to be developed code for receiving the information from the financial institution. The code will need to receive the Transaction Confirmation (Total, Token, ShoppingCart_ID, email address, Date,...) and insert into transaction log table. Also the code will trigger email send to the customer confirming the purchase. Please submit you proposal where you provide estimate of number of hour and total cost.
CMS and Admin requirements: The developed shopping cart will integrate with existing web application and calculate total exchange data with financial processing institution and update and insert data into SLQ Server existing tables.
Payment methods: Credit Card
Extra services needed: Customization
Specific technologies required: ASP.Net, VB.Net, MS SQL
Extra notes: