$10 for a 100mbps hub/switch isn't that hot... Most new motherboards are coming equipped with gigabit (1000mbps) ethernet, which will require a gigabit switch (Buy.com recently had one for $29 after rebates).
Even so, you still want a decent router between your system and the modem, because it provides a nice hardware firewall. I have a wireless 802.11g router (very cheap these days, an 802.11b could be had for $5 at CompUSA last weekend), to that, I have attached a 5 port gigabit switch (the one I mentioned), and to THAT I have my gigabit ethernet equipped PCs. Between the PCs, I get 1000mbps, and to the cablemodem, I get "whatever" it does. The other devices are switched in through the wireless router, since they only top out at 100mbps anyway.
The router provides firewalled internet access through the cablemodem, wireless connectivity for my laptop (work), and DHCP services to all of the computers on the network. The gigabit switch provides high speed connectivity between all of the PCs capable of it.
You don't need a hub for now though... a decent router also serves as a hub, too. If you get additional PCs equipped with gigabit ethernet later, you can opt to upgrade with an additional switch later, and the router will still be quite useful.
I guess, in short, I'd advise against getting a 100mbps switch/hub. Unless you can get them for free, don't bother... get a decent router instead (the wireless 802.11b routers are cheap, since it's slightly outdated... but just on the wireless side - and they usually include a 4 port wired hub integrated in)