Agreed, check out newegg.com, or tigerdirect.com, you should be able to find a decent router pretty cheap that has some switch functionality built into it. If you get a router to hide everything else behind, all your ISP will see, or should see anyway is just one IP address, so no extra monthly charges. Even with a wireless router, most of the time they come with some kind of switch/hub functionality.
In fact here ya go....http://www.newegg.com/Product/Product.aspx?Item=N82E16833314006
I have a wireless router similar to this at home, works decently for connecting my main pc to the internet, as well as giving my laptop connectivity via wireless. Also has 4 ports so you can hook up with wires the same as you are now, and then gives you that wireless for later. So it works decently. Plus it should hide your other machines behind it, so the ISP thinks you are only connecting with 1 pc. Hope it helps you out. Btw, I think it also has a little firewall functionality built in, but I'd still run software firewalls on my pc's if I were you, as well as antivirus, I reccomend AVG antivirus myself, as it's free, free updates, works ok for my needs.