Invoice for a fellow retailer at cost price

Good Morning

We’re using Shopify Online and POS Pro - is there an app or a service within our current plan where I can create a one off invoice for a fellow retailer so I can send them some of our stock with an invoice at cost price rather than full RRP? I don’t want to install an app that will change our current setup as this has worked very well for us since we began using Shopify.

Thanks in advance