I have a server with a 100 mbps port and connection that I rate limited to 10 mbps/full duplex because I am only paying for a 10 mbps connection and there are steep overage charges. Ever since then, the bandwidth has absolutely plummeted. I turned off autoneg because I otherwise would not be able to limit the rate to 10 from 100 because the network is operating so much faster. I need a way to average 10 mbps on a server with multiple users logging in on that 100 mbps port and connection. Can this be done without having these issues?
You have created a duplex mismatch. Your port is set to 10/Full and your ISP's port is set to 10/Half.
Either set your port to half-duplex (highly undesirable) or contact your ISP and ask them to set their port to 10/Full.
According to Cisco's official training material for their most basic networking certification: