If you bought a simple point and shoot or a digital camera that is fairly new, the first thing that should be done is to send it to the company that you bought it from, as part of their service. If you bought a Nikon camera for example, you should be sending it to Nikon USA. Just by looking at the website of the camera's manufacturer you will find the phone number and address of the nearest repair facility. SLR camera repair might be a bit harder if you're not from USA, but from a third world country. Still, you always have the option of sending the camera body together with your credit card number to a company that repairs digital cameras.
If the camera you want to repair is an older 35mm model that has some kind of sentimental value, then the $200 you might spend to repair it can be worth it. In this case, send it back to the manufacturer, Pentax, Nikon, whoever they might be. Now, in some cases, if the camera is way too old, they might reply that they don't have the needed parts anymore. Something like that can happen with a 20 year old camera for example. If this happens, you can contact a shop that is independent and ask them to take parts from other similar cameras that aren't working anymore, using them to repair your camera. In some cases you can even make some of those parts from scratch.