[Close] Accounting bridge

Hello,
I'm searching for an import plugin/function to import supplier/customer invoices.
Does this exist ? I was believing that in Nav there will be a standard function but there is nothing of standard in Nav.
I'm not skill in Navision and our supplier charge 7 days à 1000€ to do customer, supplier, supplier's invoice, customer's invoices import. A Little bit expensive !
The software to import from, i can produce any format file.
Thanks for your help
Yann