The latest Storefront version already support Quote feature. You simply mark your product variant Sale type = "Quote" type. The customer will not be charged and will not see the price. You can then invoice the customer separately. You can see a demo here (the user/pwd is on the Login page if you want to see how it's configured)

I hope this helps. Thanks!

Thanks, but that's not quite the functionality we're looking for. We are a private membership club and one of the options for our members is to charge their purchases to the account that gets billed monthly. So they would provide their membership number, and the payment is handled in the office through our accounting system. They are purchasing so they would need to see the price, tax, shipping charges, etc., all the same as if they were using a credit card but there's no 'card' info collected - just a membership account number. I've played with "renaming" the labels on Purchase Order to "Member Charge" and PO Number" to "Member Account" and that seems to work, I just wondered if I was missing something more appropriate...