Amazon, Ebay, Magento Invoicing Solution

Hello. I sell through EBAY, AMAZON and MAGENTO, using Paypal and other Card Payment Gateways as well as taking check payments and bank transfers. I use Sage accounts to manually retro-invoice all transactions. I have now reached several hundred transactions per week and have no time to do the invoicing. I am looking everywhere for the best solution to auto generate invoices at the point of sale (or whatever is the closest and easiest best thing). I am open to either creating individual solutions (Magento extension etc) or a solution to integrate all platforms.. I need total support to set this up as I have NO TIME sadly. Need something working fast. Please let me know if you can help. Many thanks.