Advice on custom invoice/price submission

[mmertsock]

I'm looking for a way to implement the following feature:

Show a page where the customer (not the admin) can enter one or more items for a custom invoice. Each item would have a price that can be any arbitrary number entered by the customer. The customer would then pay the total amount due based on the items entered. The idea is to let the customer pay an invoice that was received via physical mail.

 

I'm not seeing any easy way to do this sort of thing with oscommerce. Has anyone attempted something like this before? I am thinking it would be best to start from scratch for this feature and not try to force it into the oscommerce model.

 

Thanks

--M