As squarebear says, you can get crossover cables too.
Imagine the cables as being made of two wires, input and output. If you're connecting two computers together directly, you'd want the output of one to go to the input of the other. Thus, you want a crossover cable.
You want a regular cable (with no crossing) when using an old standard router, hub or switch.
However, most routers, switches and even computer ethernet ports these days are auto-switching, so it doesn't matter what cable you have, they'll adjust to work.
I find that prices range hugely. Never buy from somewhere like PC World, they're committing daylight robbery.
http://www.ebuyer.com/product/130678
About the cheapest you'll get it I'd think.