Trickle is a tool that can help you limit bandwith usage of linux command line tools such as ncftp, wget, or any other application that you may want to throttle.
From the Trickle website
trickle is a portable lightweight userspace bandwidth shaper. It can run in collaborative mode (together with trickled) or in stand alone mode.
trickle works by taking advantage of the unix loader preloading. Essentially it provides, to the application, a new version of the functionality that is required to send and receive data through sockets. It then limits traffic based on delaying the sending and receiving of data over a socket. trickle runs entirely in userspace and does not require root privileges.
Sample usage:
trickle -u 10 -d 20 ncftp
this command example ncftp limiting its upload capacity to 10 KB/s, and download
capacity at 20 KB/s.