For an office, i would go with an open source alternative on a cheap computer, like i mentioned earlier. If money is tight, you can get a $200 computer or pick up something at a yard sale, install linux (free), install squid proxy (free), and install dan's guardian (free). You now have a free monitoring server where you can block ports, internet access times, get logs of what websites visited, and more. It also will limit the possibilities of getting around the device since it is your proxy to the internet and no one has rights to change things but you. Also since it is not installed on each machine, it cant be disabled (and there is no license fee for each machine).
You just point your machines to this proxy and this proxy to the internet. It is really simple and will give you a lot more flexibility and customization at a very good price.
You could also get an all in one device from a company like astaro which will also give you other capabilities for vpn and etc.
Edit: forgot to mention... if you go with the first option, there are a lot of good resources on the web to do this, or i know people here know how to do it. It is actually quite simple and can be set up in a few hours (most of which is the install time of the OS).