With most bank lines of credit, the bank or lender requires that all payments are sent to them directly, either at the bank or by utilizing a lock box facility. In either case, the bank controls the collection process. This is usually not a negotiable item with the bank. In most cases, the bank passes through the cost of all of the fees related to the establishment, monitoring and services provided by the lock box. Again, it is quite common for the bank or lock box provider to also assess a per payment or collection fee.
It is nearly impossible to determine or provide an estimate about what these fees could cost. Each bank is different and in the event that the service is outsourced to a third party provider, it is logical to assume that the costs could be marked up by the bank to ensure some profit is earned on their relationship. If your business generated a large number of small invoices, beware that if you are charged a per collection fee, the cost could be significant.