There are freeware ways to do it, involving the use of a Linux or OpenBSD box and two network cards.
Under OpenBSD, you would set up a bridged connection and use the builtin ALTQ program to do bandwidth shaping by protocol. Everything needed to limit by protocol (eg smtp, http) is built in to the base install of the OS.
Under Linux, there is more than one way to do it.
There is a program from Mikrotik, running Linux, that has a Windows GUI control tool you may want to check out - www.mikrotik.com . I have not used it but some folks have been happy with it.
Note that if you have each web server on its own IP(even if the same physical server) it gets much easier, since you can set different rules per IP.
