There are 2 methods to evaluate costs
Quantitative - Actual visible costs
Qualitative - Hidden Customer Service costs
Assuming a very conservative 3 minutes to re-key Sales Orders into various Fulfillment and Invoicing systems leads to a grand total of 20 Sales Orders completed in 1 Hour.
Staff costs - conservatively - easily amount to $15 per hour, typically more when considering uplift costs such as Health Care and other benefits.
One staff member, assuming 8 hours workday, will be able to complete 160 orders per day.The cost is $15x8 hours = $120
At 20 days per month that amounts to 3200 orders per month.
The monthly cost of processing 3200 orders amounts to $120 per day x 20 days = $2400.
The yearly cost is $2400 x 12 months = $28,800.
The actual cost of processing Sales Orders is not the only cost. There are more significant issues created: