-A new xBox wired or unwired controller for PC costs around $30-35... and it's really good and all you really need.
-A new Razer wired controlled (basically a cooler xBox controller) costs around $70-90 and higher... I' go with the xBox controller for sure. Razer does have some cheaper ones too...
This is online, it shouldn't be any different in stores. Gamstop is pretty much the same exact price for those... xBox controllers there can be around $20 (I'd go with $30 for the xBox controller).
Not expensive at all really. And btw, you can't use a Playstation controller for PC, you can use Microsoft (xBox) controllers though. There is also Razer and Logitech, but Razer tends to get expensive for a controller, and Logitech is better known for their keyboards and wheels. They also do some decent game-pads, but I doubt that's what you're looking for. They have a $17 game-pad controller which is basically a poorer xBox controller... and some more expensive ones that are not worth the cash... y'know- just go with the xBox controller :P
If you ask me, go with the wired xBox controller 100%. I'm using a Razer Sabertooth E(lite) gaming PC controller which is basically a better, stylish, more comfortable, PC based xBox controller (even has the logo), and it costs $90 and I love it for certain controller based games... but it really doesn't get much better than $30 for a basic xBox wired controller. Razer can do specialized/custom stuff, but it's pointless...
Haha, just make sure you buy a PC controller, not an actual xBox controller. If you already have an xBox controller, they have adapters which plug in via USB.
EDIT: My bad, I forgot about that including the Playstation controller... sorry. I still wouldn't recommend it though. Third party organizations do have some PC controllers based on the Playstation controller (personally, I like the Playstation controller better, but for PC, 110% xBox controller-but that's just my [and the majorities] opinion)