Data recovery on an external hard drive?

I have a Western Digital USB external hard drive. I had it for about a year and all of a sudden the thing starts making a ticking noise when you turn it on, but when you plug it into the usb port, vista makes the sound that it detects the drive, but it does not show up and I cannot access it. I have tried all different types of data recovery software, but they also do not detect my drive. So i’m thinking about sending it to one of the data recovery labs. How exactly does this process work? and about how much would it cost me (it is a 500 gb hard drive with about 200 gb used up)? and about how long would it take for me to get my drive/files back from them?
thanks for all the answers everybody. i know that taking it to a data specialist will be pretty expensive, but around what range are we talking? and where are some of the places that I could take it to?

The actuator arm inside your drive is damaged. This is the bit that has the reading head in, a bit like an old record player that had the needle on. from what you describe it sounds like it is flicking from side to side and not able to read from the drive. Try not to run it anymore or the movement may actually erase data from the disc platter if it is low enough, or scratch it and render all the disc and data useless.
Nothing is going to software fix it and you will need to send it off to a specialist data recovery center to get your data.