I am using CRE Loaded Professional B2B v6.3.1. My client has changed his project scope and I am looking for the cleanest possible way to accommodate him.

Because he carries items that are very large and heavy, his shipping calculation is quite complicated. He would like to let the customer visit the site, add products to the cart, and instead of confirming a purchase, he wants the customer to be able to request a manually reviewed cost estimate. I can jury rig this without much of an issue by using only a payment method (like Cash on Delivery) that doesn't require the customer to enter any financial information for the estimate. But then my client wants to be able to then finish the sale via the store if the customer accepts the estimate. Does anyone know how I might go about configuring this? I'll even accept ideas to just make the estimate portion a little less ugly.

If nothing else, just tell me that nothing exists to accommodate his request so I can at least make sure he knows I covered all the bases.

get the security issues patched/plugged/upgraded to 6.4.1a first

But if the store owner wants to complete the order they would need to record payment info.. ie using a credit card module..

You could use the plain jane credit card module that just stores the cc info to process later

later versions are better at an invoice type system.. but not your version (requires the customer to log in then they can check out with the updated order invoice)