Customer Billing Section

We are a web design and development company and have a website built on Joomla. I want someone to install and integrate Customer Support section and any billing software so that we can send one-off invoices or recurring invoices to customers. The billing software should be able to support invoices in multiple currencies and should be a open source application (not custom). Please include the following details: 1. Name of OpenSource system you plan to use for billing 2. Name of OpenSource system you plan to use for customer support 3. Any similar work you may have done. 4. Include the word "Bingo" in your message so I know you have read the requirements 5. I also have some additional work I need done on the site but will be a separate project. 6. Messages with more than 4 portfolio sites will not be looked at. Budget is minimal (<$60) and cheap vendor is preferred Sandeep