Seeking traffic shaping/transparent proxy solution

[Carl Youngblood]

I am trying to find a good (hopefully free/low-price/easy) solution
for rationing bandwidth on a per-user basis to a number of downstream
wifi APs and wired clients, as well as caching downloads so that
future requests can be served locally.  NoCatSplash-type functionality
would be a good plus too.  But it needs to be in a single server,
because I will be supporting user counts that are too large to do with
individual APs, and I don't want to have to configure each AP
separately, other than to configure its wifi settings.

I've been looking at the Sputnik gateway:
http://www.sputnik.com/products/apc.html

But it doesn't seem to have any caching/transparent proxy capabilities.

Thanks,
Carl